Some of these will be inflated, but it's unavoidable I guess.

Sold for an Energy Orb Woodsy Widowmaker SMG(Well-Worn)(17 Keys) and ~6 Keys in Sweets(23 Keys total)

http://backpack.tf/profiles/76561198095448353#!/compare/1465084800/1465171200

3 Weeks unsold at 20 Keys: http://www.tf2outpost.com/trade/28173617

Only useable sale I could find, using the seller for the low end. 20-23 Keys should be fine.

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