Kinda wide range, but it may be needed for an unusual like this.

Sold for an Australium Spec KS Grenade Launcher(19 Keys with Overpay at the time) and an Australium Stickybomb Launcher(16 Keys with Overpay at the time)(35 Keys total)

http://backpack.tf/profiles/76561198056119668?time=1441868400

http://backpack.tf/profiles/76561198056119668?time=1442041200

Sold for an Australium Eyelander(29 Keys with Overpay) and a Max's Severed Head(28 Keys)(57 Keys total)

http://backpack.tf/profiles/76561198111984733?time=1442214000

http://backpack.tf/profiles/76561198111984733?time=1442559600

http://www.tf2outpost.com/trade/27013437

Sold for a Vivid Plasma Samur-Eye(39 Keys with Overpay)

http://backpack.tf/profiles/76561197987183850?time=1442905200

http://backpack.tf/profiles/76561197987183850?time=1442991600

http://www.tf2outpost.com/item/440,4155355918,359,5 Samur-Eye History

Sales seem to fit, 35-57 Keys should be fine.

Additional Proof/Counter-Proof/Constructive Criticism/Feedback is always appreciated.