A proof-less suggestion for this hat earlier inspired me to do this. You're welcome random person who owns this hat and is too lazy to look up sales to price it :P

Credit to aaroncsn for the third sale <3

Sale 1:

Sold with 4 keys for a Hellfire Rebel Rouser

(66*0.9) - 4 = 55.4 rounding to 55 keys

http://www.tf2outpost.com/trade/25683967

Seller Before: http://backpack.tf/profiles/76561198055358018?time=1429081200

Seller After: http://backpack.tf/profiles/76561198055358018?time=1428908400

Sale 2:

Sold with 3 buds, a Prof. S. Pan, and ~3 keys of sweets for a Miami Nights Hong Kong Cone (buds were 5 at the time)

(90*0.9) - 15 - 16 - 3 = 47 keys

http://gyazo.com/a07c8086a33e9e9bf99a01354cb0184e

http://www.tf2outpost.com/trade/25508932

Seller Before: http://backpack.tf/profiles/76561198029146605?time=1427958000

Seller After: http://backpack.tf/profiles/76561198029146605?time=1428044400

Sale 3:

Sold for a Stormy Storm Sammy Cap + 1 bud + 10 keys + a Prof. Australium Flame Thrower + ~5 refs in sweets. (buds were 6 at the time)

(29.5 + 28) + (6*0.95) + 10 = 67.75 rounding to 68 keys

http://www.tf2outpost.com/trade/25611607

http://backpack.tf/profiles/76561198074849590?time=1428217200 Before

http://backpack.tf/profiles/76561198074849590?time=1428476400 After

Notes:

Mini for the Prof. Strange Pan

1 sold on the SCM for $37.49 on the day of the sale

37.5/2.4 = 15.625 rounding to 16 keys

Mini for the Prof. Australium Flame Thrower

1 sold on the SCM for $66.70 on the day of the sale

66.7/2.4 = 27.7916 rounding to 28 keys

Conclusion:

Sales at 55, 68 and 47, taking the final range at 47 to 68 keys.