Finding the cheapest low-cost airline in the United States is a small exercise in financial detective work. Travelers see a $29 fare flash across the screen, immediately start planning a weekend escape, and only later discover that the advertised price barely includes the privilege of occupying a seat. By checkout, baggage fees, seat selection, and assorted add-ons have quietly transformed the ‘deal’ into something far less miraculous.
The modern budget airline industry depends heavily on this strategy of unbundling basic services into separate charges. For travelers trying to save money, the smartest approach is often to ignore the headline fare and calculate the total cost of the trip instead. In many cases, the cheapest ticket on the search page ends up nowhere near the cheapest flight by the time the payment screen appears. Read ahead.
Cheapest low-cost airline: how to compare the final price
When evaluating which carrier holds the title of the cheapest low-cost airline, you must abandon the habit of sorting search engines strictly by the lowest headline rate.
Ultra-low-cost carriers (ULCCs) operate on an unbundled business model.
They price their seats as bare-minimum transportation vessels, meaning you are essentially paying for nothing more than a physical slot on the aircraft for your body.
Base fare, baggage fees and seat selection
You need to go back and work out the actual math of an itinerary, calculating a total cost before you put in your credit card information. The total economic footprint of a budget flight can be divided into three main profit centers:
- The raw base fare: the baseline ticket price that gets indexed by search engine algorithms;
- Baggage allocation fees: the rolling cost to bring anything larger than a school backpack;
- Seat assignments: the premium structural fee levied just to ensure you aren’t assigned a middle seat in the final row.
If a competitor’s base fare is $40 higher but includes a carry-on and seat choice for free, they are often the true financial winner.
Frontier and Southwest: baggage fees and ticket rules
Spirit Airlines, long the best-known ultra-low-cost carrier in the U.S., ceased all flight operations on May 2, 2026. Frontier and Southwest still compete for the budget traveler’s attention, but their fee rules are very different.
What happened to Spirit Airlines
Spirit was the classic example of an ultra-low-cost carrier: its base ticket covered only a personal item that had to fit under the seat in front of you.
The airline stopped flying on May 2, 2026, so its fares are no longer available.
Frontier Airlines
Frontier runs on the same ultra-low-cost model and relies heavily on unbundled ancillary revenue: its basic fare includes only a personal item, and carry-on and checked bags cost extra. It enforces strict bag-sizing checks at the boarding gate using rigid metal boxes.
If your personal item handles or wheels protrude by even half an inch, agents will charge an expensive last-minute gate-checking fee.
Southwest Airlines
Southwest used to be the outlier in the low-cost space, with its ‘Bags Fly Free’ policy, but that policy ended on May 28, 2025.
Today, most Southwest fares pay for checked bags: for bookings made since April 9, 2026, the first bag costs $45 and the second $55 within the continental U.S. A-List members and Southwest credit cardholders get their first checked bag free, and Choice Extra fares and A-List Preferred members get two.
Which airline includes more in the ticket price?
When it comes to what is included in the ticket price, the answer is less clear-cut than it used to be.
Southwest dropped its free-bag policy in 2025, and its change and cancellation rules now depend on the fare type you choose, so compare them before you buy.
Southwest Airlines
- Checked bags: $45 for the first and $55 for the second on most fares (continental U.S., bookings since April 9, 2026);
- Free checked bags: the first bag for A-List members and Southwest credit cardholders, two bags for Choice Extra fares and A-List Preferred members;
- Changes and cancellations: rules depend on the fare type.
Frontier Airlines
- Personal item: free (must fit entirely under the seat in front of you);
- Carry-on bag: extra fee on the basic fare, usually higher if paid at the airport;
- Checked bag: extra fee on the basic fare, with prices that vary by route and date.
On Frontier’s basic fares, changing a flight close to departure can also add fees, so check the rules before you buy.
For travelers who check bags, the cheapest low-cost airline now depends on the fare type, the route and your status, so compare the total price with bags included before you decide.
Tips for traveling on low-cost airlines
If you fly Frontier or another ultra-low-cost carrier and want to keep your ticket cheap, your goal is to fly without adding any extras. There are some rules you can follow when trying to outsmart the checkout algorithms:
- Invest in a personal item bag: buy a soft-sided backpack designed to match the exact maximum dimensions permitted under the seat (typically 18 x 14 x 8 inches);
- Skip optional seat selection: let the airline’s algorithm assign your seat at check-in. If you are traveling as a group, accept that you might sit apart for a few hours to protect your budget;
- Print your boarding pass at home: some budget carriers charge a fee just to have an airport agent print your paper pass at the physical check-in desk. Always use the airline’s free mobile app to download your digital barcode.
Checking the real numbers
The title of cheapest low-cost airline shifts constantly depending on what you pack, when you fly, and how much comfort you are willing to compromise.
But by running an all-in price check before you buy, packing light, and remaining flexible with your dates, you can confidently navigate the domestic aviation market without falling into expensive pricing traps.
If you want to offset your travel expenses even further, smart flyers often look into converting their everyday credit card rewards into real cash to build a dedicated vacation fund.
For more carrier comparisons, hidden fee scorecards, and budget travel tips, be sure to anchor your planning at Tripiefly.
