1 of 1 in existence!

Sale 1:

Sold with 1 key for Power Surge Modest Metal Pile of Scrap (47*0.9)

X + 1 = 42.3

X = 41.3 (rounding to 41 keys)

http://www.tf2outpost.com/trade/25883462

http://backpack.tf/profiles/76561198054272311?time=1430809200 (5th May)

http://backpack.tf/profiles/76561198054272311?time=1430982000 (7th May)

Sale 2:

Sold for Max's Head (~25) + Stormy Bonk Helm (14.5*0.9) + Sweets (1.85*0.9) = 25 + 13.05 + 1.665 = 39.715 (rounding to 40 keys)

http://www.tf2outpost.com/trade/25869700

http://backpack.tf/profiles/76561198054272311?time=1430722800 (4th May)

http://backpack.tf/profiles/76561198054272311?time=1430809200 (5th May)

Conclusion:

Two valid sales at 40 and 41 keys. Taking a flat price of 40 keys.

Feel free to support/counter my suggestion!