~16 month old price!

Sale 1:

Sold for 10 keys (10) + Tinge Puffy Provocateur (1.53*0.9) = 10 + 1.377 = 11.377 (rounding to 11 keys)

http://www.tf2outpost.com/trade/25613024

http://i.imgur.com/JAfCD3N.png

Sale 2: (not using this sale, too complex and seems like an outlier)

Sold for a bunch of painted cosmetics = ~9 keys after overpay

http://backpack.tf/profiles/76561198152288799?time=1428184077 → http://backpack.tf/profiles/76561198152288799?time=1428390000

Sale 3: (invalid, can't track what it sold for; possibly SCM)

http://www.tf2outpost.com/trade/25541919

http://backpack.tf/profiles/76561198088984882?time=1427938129 → http://backpack.tf/profiles/76561198088984882?time=1427958000

Notes:

Only other one on the market has had no recent sales: http://backpack.tf/item/2761019883

http://www.tf2outpost.com/trade/25206555 - B/O of 12 keys

http://www.tf2outpost.com/trade/25642284 - B/O of 13 keys

http://www.tf2outpost.com/trade/25377152 - B/O of 13 keys

http://www.tf2outpost.com/trade/24997427 - B/O of 16 keys (~2 months)

Conclusion:

One sale at 11 keys and an invalid one at 9 keys. Also, due to previous B/O's, taking a final value of 11 keys.

Feel free to support/counter my suggestion!