Proof below (4 sales).

Sales:

http://www.tf2outpost.com/trade/14458598

-sold/bought for ge nappers+WWW+festive axe+robohat+parasite=3.8 buds taking mid prices

-set: http://www.tf2outpost.com/trade/14509770

http://www.tf2outpost.com/trade/14628332

-seems to have sold for 2 buds+21 keys=3.1 buds

-seen here:

http://backpack.tf/id/76561198060968956?time=1380351600 8 buds+31 keys

http://backpack.tf/id/76561198060968956?time=1380265200 6 buds+10 keys

http://www.tf2outpost.com/trade/14550226

-c9 cannonball sold for 6 buds+cosa

http://www.tf2outpost.com/trade/13934628

-seems to be cosa+burning phantom sold/bought for knifestorm phantom

-seen here:

http://backpack.tf/id/76561197993586962?time=1379746800 before, 4 burning phantoms, kill a watt cosa

http://backpack.tf/id/76561197993586962?time=1379833200 after, 3 burning phantoms, knifestorm phantom

-should be this duped burning phantom (level 28): http://www.tf2outpost.com/trade/13389407 and this knifestorm one: http://www.tf2outpost.com/trade/14599782

-12.5-9=3.5 buds

(knifestorm phantom hasn't sold in a while, burning phantom has had lowest past b/os of 9 buds)

Current trade:

http://www.tf2outpost.com/trade/14685773

-b/o 4.5 buds

Sales: 3.1, 3.5, 3.8, unpriced

Past trades have had 4.5-5 buds b/os. My Terror Watt Cosa suggestion was 3.5-4 buds, this is pretty similar. All sales included in suggested range.