Sale 1:

Sold for $36 on Marketplace.tf

https://marketplace.tf/items/614;5;u36

https://backpack.tf/item/933603103

No outpost

36/1.97 = ~18.3

X = 18

Sale 2:

Sold for 15 keys + Pro. KS Sharp Dresser (~2 keys, after rounding. seller re-sold it for less than 2.5)

http://www.tf2outpost.com/trade/29613396 - no or deleted B/O

Seller: https://backpack.tf/profiles/76561198202694983#!/compare/1523059200/1523145600

Buyer: https://backpack.tf/profiles/76561198394284595#!/compare/1522713600/1523145600

X = 17

Sale 3:

Quicksold, with ~1 key in items, for 14 keys

Seller: https://backpack.tf/profiles/76561198394284595#!/compare/1523145600/1523232000

Buyer: https://backpack.tf/profiles/76561198205153083#!/compare/1523059200/1523145600

X = 13

Sellers:

14 keys:

https://i.imgur.com/BWGmxyY.png

https://i.imgur.com/TXtiaJu.png - cached shows the price has been consistent for at least 10 days

https://backpack.tf/item/1406493010

Sales at:

13

17

18

https://i.imgur.com/TQFY4o0.png - quickuyers at 13+, excluding 13.

Aged seller at 14, using that as the low-end.

Going with 14-18.