Ticket prices often appear low, but once baggage fees are added in, airlines such as Allegiant, Spirit, and Frontier don't look so cheap. Depending where and when the bag is paid for, even a carry-on can cost $40 or more. In some cases, checking a bag actually costs less than bringing a carry-on. The cheapest option is to pay for any suitcases when buying the ticket; the most expensive is waiting until arrival at the departure gate.
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