This hat has never had a real suggestion before.....

There are 6 of these in existence. One is in a collector's backpack, three have never been traded before, one hasn't been traded in over a year, and there is the one I own.

http://www.tf2outpost.com/trade/16286481

Sold for 2 pure + Green Energy Rimmed Raincatcher ~ 4.2

I spoke with the person who sold the hat to the guy I bought it from. He sold it for ~5 buds in Dota 2 items, but I won't include that in the range.

http://i.imgur.com/xMgGCJC.jpg

There isn't much data on this hat, so I'll just suggest the flat price of 4.2 buds.

(Thanks to Woifi for helping me with this suggestion)