Just a thought, auction off a "model" bow with the shape and wood type, and then make the "real" one to the winners specification afterwards. That way if a hunter wants a hunting bow they can get what they want or if someone wants a light target bow, they are happy as well. I've seen spouses go for things like this, that way they aren't guessing about a gift they don't know much about. You can offer extras such as nicer wood for an additional donation to the cause (or you can just add them if the winner was very generous with their bid). Just be sure to have an actual bow at the auction, people just don't connect as well with a piece of paper stating what they would get. Like I said, just a thought.
Swamp
P.S. give the auctioneer an MSRP for the bow one way or another so they know how hard to push. Maybe a "suggested" starting bid on the bow or something if you can't talk to someone?