It cost me $65 each way with AirTran.
I too used a sherpa and it worked perfectly.
He had room to have a couple of his fave toys packed right in there with him and the zippered pockets held his vet cert, treats, leash and doo bags.
I picked up a very soft plush fleece liner to put in it ( it came with one but this one is heavenly!) and he flew in comfy style.
