According to the U.S. Department of Transportation, baggage fees brought in $1.2 billion for airlines during the first half of 2009, up from $301 million during the same period last year. In that time, bag fees have risen from $15 for the first bag to as much as $25 for one checked bag on U.S. Airways and Spirit Airlines. Those fees have carried over to other baggage -- like pets and unaccompanied children. Taking a critter into the flight cabin costs at least $69 each way on AirTran and a lofty $250 on United. While AirTran charges $39 per flight leg to escort a lone child passenger, at least four airlines charge $100 for each portion of the route. These fees are to travelers what a condo fee is to a homeowner -- built-in, mandatory costs. "One airline might have a cheaper flight, but when you add fees its gets worse," Banas says. "You really have to make this part of your comparison at this point." These fees cover only the foreseeable circumstances. Let's say the Sue Grafton novel that Bob from Toledo picked up at the airport bookstore made his carry-on bag a bit too bulky. Toting an oversized bag (more than 62 inches) can cost from $39 on AirTran to $175 on Delta, Northwest or United. Let's say that same novel made him want to stay a bit longer to finish it. Schedule changes can cost anywhere from $50 on Virgin America to $150 on six other carriers. For many holiday travelers, these and other fees are unavoidable.