If you listen closely, you may just hear a collective groan from budget travelers around the world, especially now that supposed ultra low-cost carrier Spirit has announced it will double its fee for checked luggage.

This follows on the heels of United's decision to charge $25 per extra checked bag. However disappointing these extra fees may be, United never claimed to be the budget-minded traveler's choice of transportation.

Spirit made that claim, and just like fellow budget-airline Ryanair, the airline seems to be backtracking a bit on that promise. The new charges are of course attributed to the rising cost of fuel, but when is enough going to be enough?

Now, passengers will pay $10 per checked baggage reserved online. If you wait until you get to the airport (which most people do with their luggage), you'll end up paying $20 per bag. With ticket sales that always seemed too good to be true, now we finally know why.