Sale 1:

Sold for $21 on Marketplace.tf

https://marketplace.tf/items/259;5;u7

Buyer: http://backpack.tf/profiles/76561198069149238#!/compare/1495411200/1495497600 (Looks to have sold not long after purchase)

http://backpack.tf/item/208397812

21/2.1 = 10

X = 10

Sale 2:

Sold for 9 keys + 19 ref in ~15 days

No outpost

Seller: http://backpack.tf/profiles/76561198304138933#!/compare/1492214400/1492300800

Buyer: http://backpack.tf/profiles/76561198113608582#!/compare/1491955200/1492387200

X = 10

Sale 3:

Sold for Shotgun skin (~5.5) + 3 keys in less than a day

No outpost

Seller: http://backpack.tf/profiles/76561198313483460#!/compare/1492819200/1492905600

Buyer: http://backpack.tf/profiles/76561198289322711#!/compare/1492819200/1492905600

X = 9

Sellers:

11 keys:

http://i.imgur.com/DWTx6uY.png - 5 months

http://backpack.tf/u/76561198159855421

http://www.tf2outpost.com/trade/29213662

$24.99: ~12 keys (Marketplace)

https://marketplace.tf/partneritem?sku=259;5;u7&attrib=bp

http://backpack.tf/item/193910792

http://www.tf2outpost.com/trade/29190340

Sales at:

10 (2x)

9

Sale at 9 sold in a very short amount of time, and is countered by buyers:

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

Excluding 9.

Going with 10 flat.