In 2000, the average U.S. domestic airfare cost $340. Last December, it was down to $301. So what are you complaining about?

Here's what: 

A decade ago, that $340 got you much more than a cramped seat on a crowded plane. It got you a couple of suitcases stored in the belly of the aircraft and another one or two in the bin above your head. It got you a pillow and a blanket, and even a set of headphones. It got you a hot meal, with all the soda and juice and coffee and tea your heart desired. It got you a window seat -- or an aisle seat, whichever you preferred.

Who knew those days would so quickly become the good old days? Today, the airlines can say you're paying less. But you know better. Every service or amenity offered in the not-so-friendly skies comes with a price.

"You're basically being nickeled and dimed for everything," said Brandon Macsata, executive director of the Association for Airline Passenger Rights. "The difference is night and day between 2000 and today, and it's even more if you go back to 1990."

Depending on which airline you chose, Macsata said any reasonable traveler could expect pillows, blankets, and food and drink to accompany the purchase of any ticket. But that's no longer the case, he said, as airlines continue to assign a la carte prices that can drive the cost of tickets up more than $100 per person.

"Now, there are airlines that charge you for pillows, for blankets, you're getting charged for exit rows, if you're a fat passenger," he said. "Across the board, everything has gone up. And the quality of service has not improved."

Passengers, Macsata said, are being charged for "every service under the sun." 

On Tuesday, Spirit Airlines took a la carte to a new level, announcing that beginning Aug. 1 it will charge from $30 (if paid in advance) to $45 to store a carry-on bag in the overhead storage bin -- and only one bag per passenger. It marks the first time an airline will charge passengers to carry their own possessions onto planes.

According to Department of Transportation statistics, airlines pocketed $1.9 billion in baggage fees in just the first nine months of 2009, with Delta Air Lines leading the way. That's up from $464 million in 2007.

And while Spirit may be the first to charge for carry-on items, it certainly won't be the last -- unless passengers fight back, an advocacy group told FoxNews.com.

"If there's not a lot of public outcry about this and Spirit Airlines' seats are still full, then other air carriers are going to do it too, period," said Kate Hanni, executive director of Flyers Rights, which bills itself as the largest nonprofit consumer organization representing U.S. airline passengers. 

"It's a racket. It's a total scam that the airlines have when it comes to baggage. It's a total scam."

Hanni said the steadily rising cost of traveling with luggage is the second most common complaint she hears from passengers, topped only by flight delays.

"This is a very widespread issue," Hanni said. "People are ticked off. They feel like they're being taken everywhere they turn."

"What's next?" she asked. "Paying for toilets? Trust me, they're going to go as far as they can push it," she said.

In fact, a European discount airline, RyanAir, is planning to start charging passengers about $1.50 just to use the bathroom on flights, the Daily Mail reported. RyanAir is working with Boeing to develop coin-operated toilets that would accept Euros and British pounds and hopes to have 168 planes outfitted by the summer.

"The airlines have a history of callous disregard for airline passengers," Hanni said. "They just don't care. It's all about their margins."

A spokeswoman for Delta Air Lines declined to comment when asked if the company will begin charging for carry-on bags. Representatives for American Airlines and United Airlines did not return messages seeking comment.

But Brad Hawkins, a spokesman for Southwest Airlines, which is the only major carrier that still doesn't charge for storing luggage, said there's "absolutely no way" the Dallas-based carrier will follow Spirit's lead.

"Our competitors continue to differentiate themselves as a pack away from Southwest, and our customers continue to tell us in the way they buy tickets and the way they give us feedback that they believe that certain things should come with the value of the ticket," Hawkins told FoxNews.com. 

"We love their bags -- the two they get to check for free and especially the ones they don't mind carrying on themselves."