The price of this hat is 5 months old. A lot of Fancies seem to be in need of an update as well.

Hat #1

http://www.tf2outpost.com/trade/9382446 Owner of hat before current owner

Current Owner bought it for: 2 buds and 3 painted Bills (Spirit, Debonair, and Overalls 27 keys)

There are other good offers, but they are all 2 months old. These include: 56 keys, Level 62 TS Max, Clean Max + TS Bills, SF Rocket, Blizz Veil (2.1-2.5 buds).

http://www.tf2outpost.com/trade/10947624 Current Owner's old trade

Offers: Orbiting Fire Cold Killer (2.4-2.8 buds), 2 buds pure, Orbiting Fire Cosa + Nuts Brown Bomber painted Spectrum (2.4 buds-2.7 buds. I know the Spectrum adds more, but I don't know how much).

http://www.tf2outpost.com/trade/11411804 Current Owner's current trade, no offers stand out.

Conclusion: Sorry I couldn't find more than 1 hat, but I think this is ample proof. I think a good low range is 2.1 buds because of the 56 key, 2 buds, SF Rocket, and 62 TS Max offers. 2.5 as high end due to Orbiting Fire Cold Killer and Blizz Veil offers. I consider the Nuts Bomber + Orbiting Cosa as an outlier. Please comment if you think I did something wrong, if I get lots of downvotes I at least want to know why.