One of one hat here, it has sold 3 times so far.

http://www.tf2outpost.com/trade/12865198 - offers of:

-Searing Gatsby(~20 keys) + 10 keys + O.Fire Elfin Deal(~17 keys) + P Fetti Stuntsman(~13 keys) = ~2.7 buds

-Bliz Brigade(~1.3) + P Fetti Mancer(~1) = ~2.3 buds

-Bliz Mancer(~.1.5) + Steam Bonk Boy(~2.9) = ~4.4 (outlier? retracted? or outdated prices? no other offers come near this)

Sold for a L1 Max Head(~2 buds)

Timestamp: http://backpack.tf/id/76561198061020427?time=1374822000

http://www.tf2outpost.com/trade/13090975 - B/O 5 buds

-offered Phosphorus One Man Army(~2.7 buds)

Sold for Eerie Crocoleather(~1.8 buds) + Steaming Engie Cap(~13 keys) + 13.5 keys in sweets = ~3 buds

Proof

Timestamp: http://backpack.tf/id/76561198059233881?time=1375167600 - Sold to Misik

Sweets were: http://www.tf2outpost.com/trade/12917882 and http://www.tf2outpost.com/trade/13153171

History in timestamp links all these items to Gucwindur.jpg, guessing he's an alt of Misik or something.

http://www.tf2outpost.com/trade/13211412 - B/O 8 buds

Sold for Miami Nights L'Inspecter

http://www.tf2outpost.com/trade/13355753 - B/O 6 buds, offers of:

-Heart Tavish Degroot(~3 buds)

-Time Warp Soldered Sensei(~2.7 buds)

Price Talk

The first owner sold for around 2, however, he had many offers exceeding that. This begs the question why he sold for so little. For this reason I believe 2 is too low to include in the range. The second sale was for ~3 buds, and the current owner has offers that are equal or come close to that(but not exceeding it). Since 2.7 is a commonly offered amount, I made it the low end.