Going with the sale where the hat was not offered, as that seems like it should be more indicative of the hats true value

Sale #1

http://www.tf2outpost.com/trade/22137432

Sold for Aces BoA + TF Logo Grimm + a bunch of stuff worth about 22 keys

http://backpack.tf/profiles/76561198110680534?time=1424332800

49 + 18 + 22 = 89 keys * 0.9 = 80 keys

Sale #2

http://www.tf2outpost.com/trade/25352400

Offered with 24 keys on a PE phantom

67 – 24 = 43 keys

TF Logo Grimm mini

http://www.tf2outpost.com/trade/25344760

Sold for a spec. aussie blackbox, 20 keys * 0.9 = 18 keys