No previous passed suggestion. Proof based on 5 sales in the last month + 1 c/o. Sales range from 13-28, but most reliably between 16-21.

15 keys in unusuals: http://www.tf2outpost.com/trade/9797974 - willing to trade for peace dread knot

16 keys pure - http://www.tf2outpost.com/trade/9714226

18.5 keys in unusuals - http://puu.sh/2xiQx/429f7c48d3 (courtesy lovedragon)

19 keys pure - http://www.tf2outpost.com/trade/9132832

23.5 keys in unusuals - http://www.tf2outpost.com/trade/9906612 - offer of smoking rack

31 keys in unusuals - http://www.tf2outpost.com/trade/8456768 - sold for nuts buto (1.2 in unusuals)

Conclusion: Highly variable sales/offers. The 15 and 31 in unusuals are outliers on either end. Using 16-21 as a more reliable indicator of its true value since most reasonable offers, trades occur in that range.

Honestly, Chief Shoe's suggestion was close enough, he could have kept it up - http://backpack.tf/vote/id/5164d82b4bd7b8ab2a000011