Sale 1:

Sold for Orbiting Fire Stainless Pot (15.5)

No outpost

Seller: https://backpack.tf/profiles/76561198127156948#!/compare/1499731200/1499990400

Buyer: https://backpack.tf/profiles/76561198179133886#!/compare/1499731200/1499990400

X = 16

Sale 2:

Sold for $31.35 on Marketplace.tf

https://marketplace.tf/items/319;5;u35

https://backpack.tf/item/1657603911

31.35/2.04 = ~15.4

X = 15

Sale 3:

Sold for Tesla Coil Wing Mann (11.5) + 2 keys + revolver

No outpost

Seller: https://backpack.tf/profiles/76561198328964908#!/compare/1497916800/1498003200

Buyer: https://backpack.tf/profiles/76561198181076763#!/compare/1497657600/1498003200

X = 14

Sale 4:

Bulk for Vivid Plasma Crocleather

Seller: https://backpack.tf/profiles/76561198122571560#!/compare/1500422400/1500508800

Buyer: https://backpack.tf/profiles/76561198125791160#!/compare/1500422400/1500508800

Should be used on the Crocleather.

Sellers:

15 keys:

http://i.imgur.com/swX2AsZ.png

http://www.tf2outpost.com/trade/29198200 - 1 month

20 keys:

http://i.imgur.com/107TYrZ.png - 3 days

Sales at:

14

15

16

Going with 14-16.