Proof below (5 sales). Overpay is applied.

Prices used are of time of sale.

1st sale:

http://www.tf2outpost.com/trade/14202921 sold for stormy wraith wrap+smoking big elfin deal here: http://www.tf2outpost.com/trade/14233138 =~4 buds

2nd sale:

http://www.tf2outpost.com/trade/14171714 sold for dp salty dog, which has been sold/bought for smoking muffs: http://www.tf2outpost.com/trade/13858938 , making the cosa ~3.8 buds

3rd sale:

http://www.tf2outpost.com/trade/13034870 bought planets phantom+vivid mullet=~3.8 buds (based on trade prices)

4th sale:

http://www.tf2outpost.com/trade/12417613 ghosts beret+big kill sold/bought for this cosa: http://www.tf2outpost.com/trade/12838787 =~3.5 buds

5th sale (unknown price):

http://www.tf2outpost.com/trade/13558522 sold/bought for #2 staff+stormy bubble pipe (2.4) seen here: http://www.tf2outpost.com/trade/13750616

Sales: 3.5, 3.8, 3.8, 4

Any help regarding the price of the #2 staff would be greatly appreciated. All known sales are within suggested range.