Proof below (4 sales).

Sales:

http://www.tf2outpost.com/trade/14588389

-sold for b/o

-buyer's bp:

http://backpack.tf/id/76561198049844846?time=1381302000 2 buds+60 keys

http://backpack.tf/id/76561198049844846?time=1381388400 cold killer+1 bud

-1 bud+60 keys=~4.3 buds

http://www.tf2outpost.com/trade/14938415

-b/o of 7 buds

-seems to have sold for steaming luchadore+46 keys

-seller's bp:

http://backpack.tf/id/76561198049844846?time=1381388400 cold killer

http://backpack.tf/id/76561198049844846?time=1381474800 steaming luchadore+46 keys

-~3.6 buds

http://www.tf2outpost.com/trade/13156333

-quicksold for 3 buds, had 5 written adds

http://www.tf2outpost.com/trade/12927172

-wanted offers, 2 months ago

-sold for dbd trilby (unpriced)+gbh berliner's (2.48)+planets tam (0.77), trilby is around 5, making this sale 8+ buds, obvious outlier

Current trades:

http://www.tf2outpost.com/trade/14969846

-b/o of 8 buds

http://www.tf2outpost.com/trade/13646089

-offers

http://www.tf2outpost.com/trade/13187808

-wants 8 buds, 2 months old

Priced sales: 3, 3.6, 4.3

The sale at 3 buds had 5 written adds all willing to pay 3 buds, so I'm not including it in the range as it's a bit low. The 8 buds sale is also very high and 2 months old and looking at the already overpriced current b/os and sales this shouldn't be in the range.

The last 2 sales form the high and low ends.