Hella old price. Just taking 11 and 12 out because of the amount of offers at 13 and the sales at 13 and 15.

Let's start with sales!

I bought mine on a quicksell for 10 keys, and sold for a nuts little buddy (11-12 keys) , a s.f. sapper which at the time was priced at 5 keys (though it dropped that same day to 4-4.5 so I will use this as a more accurate estimate) and a key.

http://imgur.com/a/NQ7Sx

11.5*0.9+4.25*0.9+1 = 15.175, high end of 15 keys seems pretty valid.

http://www.tf2outpost.com/trade/16577488 - sold for 13 keys in under 40 views.

And on to some offers:

http://www.tf2outpost.com/trade/15766483

11 keys is offered and not taken.

offered 13 keys, also offered a steaming larrikin "if you maybe add a key" (unclear whether the adding of a key is part of that, either way it's ~12/13 after overpay.)

http://www.tf2outpost.com/trade/16724485

11 keys is offered and rejected.

http://www.tf2outpost.com/trade/16684856

13 keys offered

http://www.tf2outpost.com/trade/16724901

13 keys and a high five taunt, ~14 keys.

with the number of offers at 13 keys and the sales potential above, 11 and 12 keys do not belong in the range.

Please tell me in very great depth why I'm wrong and stuff :)