What happened: You bought a cheap nonrefundable ticket, but a sudden illness forced you to cancel or postpone your trip. Now the airline is charging you $100 to change your travel dates, plus the difference between what you originally paid and the current, much higher fare.

What the airline should do for you: Nothing. If you want to pay for ultra cheap tickets then you run the risk of paying a hefty fee and a fare increase if your plans change.

Next time: Fly a budget carrier. Southwest Airlines is the only carrier that doesn’t levy a penalty on changing a nonrefundable ticket. Instead, they apply the ticket’s full value toward a future flight taken within a year of the original departure date. Most of the other discount carriers also have low change fees, but the standard carriers charge up to $100 for domestic-flight changes and $200 for international ones. Almost all airlines will make you pay any fare increases.