7 month old price!

Sale 1:

Sold with Professional Australium Sniper Rifle for Gifted Professional Australium Sniper Rifle

http://www.tf2outpost.com/trade/26469770

http://backpack.tf/profiles/76561198045752247?time=1436857200 (July 14th)

http://backpack.tf/profiles/76561198045752247?time=1437116400 (July 17th)

Sale 2:

Sold for 11 keys

http://www.tf2outpost.com/trade/26561533

http://i.imgur.com/u85q4tm.png

http://backpack.tf/profiles/76561198070605773?time=1437634800 (July 23rd)

http://backpack.tf/profiles/76561198070605773?time=1437791399 (July 25th)

Notes:

Surprisingly, there are no other recent sales.

http://www.tf2outpost.com/trade/26580870 - B/O of 12 keys (young)

Conclusion:

One valid sale at 11 keys. Taking a final value of 11 keys.

Feel free to support/counter my suggestion!