First time doing a price suggestion...sorry if it's wrong. I've looked at a lot of stuff and this should be right though. Since it is a 1 of 1 hat that isn't going to be on the market anytime in the forseeable future, this only recent sale should be enough.

1 of 1 in existence sold for 80 keys (5 buds at current bud price) to the best Pencil Pusher collector ever who is not planning to sell any of his collection anytime in the near future: http://www.tf2outpost.com/trade/20139556

(*insert obligatory "owns one, obviuz price manipulation here"*)