I received my mastiff puppy via American Airline. She was 8 weeks and it cost about $400. The flight went from MO to AZ. It had mechanical problems and turned into a 8 hour trip for her. She was fed, given water and walked mulitple times between the transfer, and came to us in good spirit. I don't know how I would feel about getting a yorkie via the same way because they are more fragile then my mastiff puppy was.
but all in all I was impressed by the care they gave her, and she was hand delivered to me from an american airlines employee, with a log attached to her carrier of when she was fed, and walked through out the trip.