Using last month.

Sale 1:

Sold for $28 on marketplace.tf

https://marketplace.tf/items/1106;5;u3004

28/1.97 = ~14.2

X = 14

Sale 2:

Sold for 11 keys

Seller: https://backpack.tf/profiles/76561198002757046#!/compare/1525910400/1525996800

Buyer: https://backpack.tf/profiles/76561197993564909#!/compare/1525910400/1525996800

Some keys appear on the seller’s end, some appear on the buyer’s end (9 total), some I had to find manually:

https://backpack.tf/item/6839207681

https://backpack.tf/item/6839207694

X = 11

Sale 3:

Sold to a bot for 9 keys + 16 ref

Seller: https://backpack.tf/profiles/76561197970562002#!/compare/1525132800/1526083200

Buyer: https://backpack.tf/profiles/76561198344933095#!/compare/1525651200/1525910400

Bot.tf confirms: https://i.imgur.com/KmoVDlx.png

X = 9.5

Sellers:

13 keys:

https://i.imgur.com/W8Vb10i.png

https://backpack.tf/item/3246058173

19 keys:

https://i.imgur.com/OUJog37.png

https://backpack.tf/item/3893394477

Sales at:

9.5

11

14

Gonna excluding 9.5 and 14 and go with a flat value here, because 9.5-14 is a silly range.

Going with 11 flat.