Using last 2 months.

Sale 1:

Sold for $23.90 on Marketplace.tf

https://marketplace.tf/items/30922;5;u3008

23.9/1.98 = ~12.07

X = 12

Sale 2:

Sold for 9 keys

Seller: https://backpack.tf/profiles/76561198121830870#!/compare/1521849600/1521936000

Buyer: https://backpack.tf/profiles/76561198302382325#!/compare/1521849600/1521936000

X = 9

Sale 3:

Sold, most likely to a quickbuyer, for 7 keys + 14 ref

Seller: https://backpack.tf/profiles/76561198126703469#!/compare/1521417600/1521504000

Buyer: https://backpack.tf/profiles/76561198119563409#!/compare/1521331200/1521417600

X = 7.5

Sale 4:

Sold with Killstreak pan kit for Blizzardy Storm Hetman’s Headpiece

Seller: https://backpack.tf/profiles/76561198143320939#!/compare/1521244800/1521331200

Buyer: https://backpack.tf/profiles/76561198180728714#!/compare/1521244800/1521331200

Easily fits in the range.

Sale 5:

Sold for Miami Nights Conquistador

No outpost

Seller: https://backpack.tf/profiles/76561198180728714#!/compare/1521331200/1521417600

Buyer: https://backpack.tf/profiles/76561198126703469#!/compare/1521072000/1521331200

Seems high, especially without a B/O, excluding.

Sellers:

18 keys:

https://i.imgur.com/q1fDKgC.png

https://backpack.tf/item/6549777100

And 2 sellers on the SCM for ~10 keys worth:

https://i.imgur.com/vs4BELP.png

Sales at:

9

12

Going with 9-12.