St. Louis on a Shoestring: Your Guide to the Best Budget Airlines for 2025

St. Louis Lambert International Airport (STL) has quietly become a stronghold for affordable air travel, thanks to a healthy mix of low-cost carriers that know how to keep fares down. If you’re hunting for a spontaneous weekend trip or a carefully planned vacation, choosing the right budget airline can mean the difference between a $49 ticket and a $249 one—often on the very same route. The best budget airlines flying from St. Louis in 2025 are Southwest Airlines, Frontier Airlines, Spirit Airlines, and Allegiant Air. Each one works differently: some include bags, some don’t; some serve major business cities, others focus on warm-weather getaways. Understanding those differences will help you book the flight that fits your wallet and your travel style without locking you into a trip full of hidden fees.

St. Louis Lambert International Airport is one of the country’s most user-friendly midsize airports, with two terminals and a manageable layout that rarely overwhelms. More than 10 airlines offer service from St. Louis Lambert International Airport, but the four budget carriers spotlighted here account for a huge share of the airport’s low-fare inventory. Whether you want the free-flowing flexibility of Southwest, the rock-bottom base prices of Spirit and Frontier, or the vacation-focused routes of Allegiant, you have plenty of paths to saving money without giving up convenience.

This guide breaks down exactly what you need to know about each airline, the destinations they serve from STL, and how to find the cheapest possible ticket without falling into the common traps that inflate budget fares. Use the tips and strategies on timing, booking, and baggage to keep your total travel cost exactly where you want it: low.

Top Budget Airlines Flying from St. Louis Lambert International Airport

STL is not dominated by any single low-cost giant; instead, it hosts a competitive mix that pushes all four to keep base fares aggressive. Each carrier has strengths and quirks, and picking the right one depends on what matters most to you—whether that’s a network of nonstop routes, genuinely inclusive pricing, or the absolute cheapest ticket possible even if it means adding on every extra.

Southwest Airlines: Bags Fly Free and Fare Flexibility

Southwest is the hometown favorite for many St. Louis travelers, and it’s easy to see why. The airline lets every passenger check two bags for free, an increasingly rare benefit that can save a family $120 or more round-trip compared to competitors that charge per bag each way. Southwest also doesn’t charge change fees: if your plans shift, you only pay the difference in fare (if any). The Rapid Rewards frequent flyer program is straightforward, points don’t expire as long as you keep the account active, and there are no blackout dates on award tickets.

From STL, Southwest operates a robust schedule of nonstop flights to cities across the country, including Chicago Midway, Denver, Dallas Love Field, Phoenix, Las Vegas, Orlando, Atlanta, and many more. The open seating policy means you board by group and choose any available seat, which can be a love-it-or-hate-it part of the experience—but it also keeps boarding efficient. Fares consistently undercut traditional carriers on competitive routes while keeping the experience predictable. For travelers who want low fares without a constant stream of add-on fees, Southwest is the strongest pick from St. Louis.

Frontier Airlines: Ultra-Low Base Fares With À La Carte Options

Frontier has expanded its presence significantly at St. Louis Lambert and now connects the city to more than a dozen destinations with fares that can drop below $30 one-way during a sale. The airline works on an unbundled model: the ticket covers a seat and one small personal item, while everything else—carry-on bag, checked luggage, seat selection, and even in-flight drinks—costs extra. This keeps the base price honest, but the final total can climb quickly if you aren’t careful.

Frontier’s network from STL serves major cities like Denver, Las Vegas, Orlando, Phoenix, and Miami, along with secondary airports that bypass big-city congestion. The Frontier Airlines frequent flyer program FRONTIER Miles and the Discount Den fare club (which charges an annual fee for access to lower members-only fares) can help frequent travelers save. The airline’s modern Airbus fleet and on-time record have improved in recent years, and if you pack light—truly just a backpack that fits under the seat—you can travel for an unbeatable price. Just budget for any extras up front so the “cheap fare” stays cheap.

Spirit Airlines: The Bare Fare Plus What You Need

Spirit Airlines brings its no-frills approach to a growing list of routes from St. Louis, often competing head-to-head with Frontier on popular leisure corridors. Like Frontier, Spirit sells a very low base fare and charges for nearly everything else, including carry-on bags (overhead bin space), checked luggage, and onboard snacks. Spirit’s Big Front Seat is a notable upgrade—essentially a domestic first-class-size seat at a fraction of what legacy airlines charge for extra legroom—but you still pay à la carte for bags and boarding priority.

From STL, Spirit flies to Fort Lauderdale, Orlando, Las Vegas, Los Angeles, and Tampa, among other sunny spots, and often adds seasonal routes during peak demand. The Spirit Airlines Free Spirit loyalty program and the Saver$ Club subscription (which gives discounts on fares and bags for a yearly fee) can bring costs down further for repeat travelers. Spirit’s strict personal item sizing is famous—always double-check dimensions before you fly to avoid a gate fee. When you treat the bare fare as a base and only add the options you actually need, Spirit can deliver an incredibly low total price.

Allegiant Air: Sun-Soaked Leisure Routes With a Small-City Focus

Allegiant takes a different path from the others by focusing almost exclusively on vacation destinations, often flying to smaller airports that put you right near the beach or resort area. From St. Louis, Allegiant connects travelers directly to popular warm-weather spots in Florida, including Punta Gorda/Fort Myers, Destin/Fort Walton Beach, and Orlando/Sanford. The routes are typically flown a few times per week rather than daily, so you’ll need to build your schedule around Allegiant’s calendar.

The airline’s pricing model is similar to other ultra-low-cost carriers: base fares are low, but you pay for assigned seats, checked bags, carry-on bags, and even a soda on board. Allegiant packages vacations—flights plus hotel—that can be competitively priced, and the Allegiant Air Allways Rewards program offers points on spending. The key to Allegiant is knowing that its sweet spot is nonstop weekend escapes to the sun; if you can pack a personal item only and don’t mind the less frequent schedule, you’ll score a trip that’s hard to beat on price.

Exploring Destinations: Where You Can Fly for Less from STL

St. Louis Lambert offers an impressive map of nonstop destinations spread across the country, with budget airlines covering many of the most popular vacation and business routes. Whether you’re looking for a quick direct flight to a major hub or a seasonal nonstop to a beach town, the airport’s low-cost carriers have you well covered.

Coast-to-Coast Nonstop Connections

The combined networks of Southwest, Frontier, Spirit, and Allegiant serve more than 50 nonstop destinations out of St. Louis, with frequent flights to Denver, Las Vegas, Orlando, Phoenix, Dallas, Atlanta, and Chicago. Southwest alone operates a dense schedule to business and leisure cities alike, while Frontier and Spirit fill in with complementary frequencies that keep pricing competitive. This overlapping coverage means you can typically find at least one low-fare option on popular pairings like STL to Denver, where multiple budget carriers vie for your business.

Beyond the obvious spots, routes to Fort Lauderdale/Miami, Tampa, and Los Angeles appear on Spirit and Frontier boards, and Allegiant tosses in its own nonstop links to smaller Florida airports. The total number of nonstop destinations from Lambert hovers around 70, with budget airlines collectively serving the lion’s share of the airport’s lowest fares. That kind of direct accessibility means you can fly to a meeting in Dallas Love Field, then turn around and book a Florida beach trip without ever connecting through a crowded mega-hub.

Seasonal Sun and Holiday Getaways

Budget airlines from St. Louis really shine when you want to escape during the cold months or travel over school breaks. Frontier, Spirit, and Allegiant all ramp up seasonal service to Florida, adding frequency and occasionally new nonstop markets between November and March. Myrtle Beach, Punta Gorda, and Sanford/Orlando see extra flights timed exactly for spring break and winter sun-seekers, often at fares that look too good to pass up.

Some years, the airlines also test international seasonal routes from STL to Cancun or Punta Cana, though these can shift year to year. The best way to catch these limited-run flights is to sign up for airline email lists or watch their route announcements in late summer when winter schedules are unveiled. Because seasonal capacity is finite, early booking usually yields the best price—waiting until the holidays are right on top of you could leave you paying a premium for a seat that was half the price six weeks earlier.

Regional Hubs and Small City Connections

While the flashy coastal routes get attention, budget carriers also connect St. Louis to regional destinations that matter for visiting family or attending events in smaller cities. Southwest’s network reaches Midway in Chicago, Nashville, and Birmingham, while Frontier and Allegiant occasionally add service to spots like Austin, San Antonio, or secondary airports near larger metro areas. These regional links can be convenient for avoiding long drives and the hassle of connecting at a massive hub when a direct, low-cost flight exists.

Budget carriers often choose smaller or alternative airports to keep costs down—think Chicago Midway instead of O’Hare, or Orlando Sanford in place of the main Orlando International Airport. That can work in your favor if your final destination is closer to those gates, but always check ground transportation options before booking. The good news is that STL’s central location makes these regional hops reliably short and often surprisingly affordable.

Smart Strategies to Score the Lowest Fares from St. Louis

Getting the ticket price you brag about to friends isn’t pure luck. A few deliberate habits and the right tools can consistently push your fare down, sometimes by hundreds of dollars on the same route. The golden rule: flexibility is the single biggest money-saver, followed closely by knowing where and when to book.

Embrace Flexibility: When to Fly and When to Book

Flying on Tuesdays, Wednesdays, or Saturdays almost always yields lower fares than peak Friday and Sunday travel. Budget airlines set their pricing algorithms to reward passengers who can shift their departure or return by just a day or two. Early-morning and late-night departures can also carry smaller price tags, even if they’re less convenient. Use the flexible date search tools built into the airline websites or on aggregators like KAYAK to view a 7-day fare grid—it’s one of the fastest ways to spot the cheapest day to fly.

When you book matters, too. For domestic budget carriers, the sweet spot is usually one to three months in advance. Booking too early can mean paying a higher introductory fare, and booking too late—within two weeks—often triggers a spike as the flight fills. Set a reminder for when you’re inside that booking window, and be ready to buy when you see a fare drop that meets your target price.

Always Check the Airline’s Own Website

After you’ve scanned an aggregator, go directly to the airline’s site before you pull out your credit card. Many budget carriers offer web-only deals, fare club discounts, or bundles (like a bag plus seat selection) that third-party booking engines can’t display properly. Booking directly also gives you a direct line to customer service if your flight is canceled or delayed, rather than getting stuck in limbo between the airline and an online travel agency.

Southwest flights, for example, do not appear on most fare comparison sites at all. You have to visit Southwest.com to see its prices and book. Loyalty program benefits and points are also easier to manage when you book direct, and seat selection (where applicable) is instantly confirmed. Staying in the airline’s own ecosystem often saves hidden fees and removes the mystery third-party fees that can appear at checkout.

Master Fare Comparison and Alerts

You don’t need to stare at a screen refreshing prices every hour. Fare comparison tools like Skyscanner, Google Flights, and Airfarewatchdog let you set price alerts for your preferred routes from St. Louis. When fares dip, you get a notification and can book immediately before the price bounces back. Because budget airlines like Frontier, Spirit, and Allegiant frequently run flash sales—sometimes with fares as low as $19 one-way—an alert can be the difference between catching the deal and missing it by an afternoon.

Cross-checking two or three sources remains a smart habit. An individual aggregator might not show prices from every low-cost carrier, or it may estimate a bag fee higher than the airline’s current bundle. Once you find a fare that looks promising, open the airline’s site in a private browsing window to see the real final price with your chosen add-ons. This final sanity check confirms that the “cheapest” flight on the comparison site actually stays cheap after bags and seat selection.

Join Loyalty Programs and Fare Clubs

Frequent budget airline travelers from St. Louis should seriously consider joining each carrier’s loyalty program—it’s free and often yields discounts or priority access during sales. Southwest Rapid Rewards, Frontier FRONTIER Miles, Spirit Free Spirit, and Allegiant Allways Rewards all let you earn points on every flight and redeem them later. Even if you fly once a year, you can bank points or take advantage of member-only fare sales.

Beyond free programs, subscription-based fare clubs can pay off quickly. Frontier’s Discount Den (about $60 per year) unlocks lower members-only fares, and Spirit’s Saver$ Club offers similar savings on tickets and bag fees. If you fly from STL to Florida even twice a year, the math often works out. Just run the numbers against your typical travel patterns before you subscribe, and remember to renew only if you’re booking enough trips to justify the fee.

Decoding Budget Airline Fees: Bags, Seats, and More

A $39 ticket can double if you breeze through checkout without noticing the optional extras that aren’t really optional for your trip. Knowing how each airline handles baggage, seating, and boarding can stop that from happening.

Checked and Carry-On Bag Fees

Southwest is the clear winner here: two checked bags free, and a carry-on plus personal item at no cost. Frontier, Spirit, and Allegiant all charge for carry-on bags that go in the overhead bin and for checked luggage. Their fees are lowest when you pay during the initial booking, higher if you add bags later online, and most expensive at the airport. A carry-on bag on Frontier or Spirit might cost $30 to $60 each way if you pay in advance, but can jump to $99 at the gate. Pack only a personal item that fits under the seat, and you’ll avoid the fee entirely.

Allegiant’s bag fees are structured similarly, and checked bag prices rise significantly if you wait until at the airport. Always check the airline’s detailed baggage page before you pack; dimensions and weight limits are enforced strictly, especially on the ultra-low-cost carriers.

Seat Selection and Boarding

Southwest’s open seating means you never pay extra for a standard seat, though EarlyBird Check-In ($15–$25 per person each way) automatically checks you in and can snag a better boarding position. On Frontier, Spirit, and Allegiant, picking a seat costs extra—ranging from a few dollars for a random assignment up front to $50 or more for an exit row or Big Front Seat. If you don’t pay, you’ll be assigned a seat at check-in, which might separate traveling companions. Budgeting for at least one seat selection, especially if you’re flying with kids or prefer a window, can reduce stress.

Other Extras: Drinks, Wi-Fi, and More

In-flight beverages and snacks are complimentary on Southwest, but they’re purchase-only on Frontier, Spirit, and Allegiant. If you want Wi-Fi, Southwest offers it for a flat fee ($8 per device on most flights), while the others may have limited or no connectivity. Some bundle options—like Frontier’s “The Works” or Spirit’s “Flight Flex”—combine a bag, seat, and boarding priority at a discount. Review these bundles at checkout; they can sometimes lower the total cost compared to adding items individually.

Ready to Book Your Cheap Flight from St. Louis?

St. Louis travelers have more affordable flight options than ever, and the key to making the most of them is matching an airline’s strengths to your own trip priorities. Southwest’s all-in pricing and free bags make it a no-brainer for families or anyone who hates nickel-and-dime fees. Frontier and Spirit offer the absolute cheapest base fares for those packing light and staying flexible, while Allegiant excels at direct flights to sunny vacation spots when your schedule can align with its less-than-daily frequencies.

Before you click “purchase,” take sixty seconds to compare the total cost—base fare plus the add-ons you know you’ll need—across at least two airlines. Check the airline’s own site, set fare alerts on a tool like Skyscanner, and if your travel window allows, nudge your dates toward the middle of the week. With a little planning, the budget carriers flying from St. Louis Lambert International Airport can get you to beaches, mountains, and big-city downtowns for a price that leaves plenty of cash left over for the fun part of the trip.