I am a fairly new builder but it certainly looks like you got screwed. It sure seems like thats a lot for a profile plane. It also might be that the guy is a crook and simply does not want to give you the plane back...he might be flying it right now for all you know and he is hoping that you will tell him to keep it. I build because I love to build. I would have done it for $200 too but like was already stated you dont expect to get paid for things you like doing.

However it is your fault because you didn't work out agreements ahead of time for a cap price or at least an estimate of the total time. You agreed to the hourly cost so you should pay the bill. You might can negotiate the hours and ask for a detailed timesheet if he does not come off the 65 hours. I too would pay it and take it in the hind end.