4 of these in existence, 3 are up on outpost and have sales.

http://www.tf2outpost.com/trade/11349515 (3 month old sale)

Sold for Self Made Key(~4.8 buds)

http://www.tf2outpost.com/trade/13590518

-offered self made key (recently)

http://www.tf2outpost.com/trade/12631440

-offered 3 buds

http://www.tf2outpost.com/trade/13949220

Sold with a Scorching Western Wear(~2.9) and small sweets for a Time Warp Headwarmer(~7)

7 - 2.9 - 0.1 = ~4 buds

Proof: http://backpack.tf/id/76561198067943926?time=1377586800

http://www.tf2outpost.com/trade/12012844

Sold with Overlocked Oiled Baker Boy(no price) for Planets Brotherhood(~7.1)

Using guestimation this probably puts the sale a bit below 5.

http://www.tf2outpost.com/trade/11129010 (2 months ago)

apparently sold for money