Using last month.

Sale 1:

Sold for $16.50 on marketplace.tf

https://marketplace.tf/items/1110;5;u3007

http://manic.tf/keyprice/?at=2018-09-21 - $16.50 / $1.84 = 8.97 keys

https://backpack.tf/item/3445386448

X = 9

Sale 2:

Sold for 9 keys

Seller: https://backpack.tf/profiles/76561198164651434#!/compare/1537315200/1537401600

Buyer: https://backpack.tf/profiles/76561198182591411#!/compare/1537401600/1537488000

https://backpack.tf/item/2860084869

X = 9

Sale 3:

Sold to a bot for 6 keys + 10 ref?

Seller: https://backpack.tf/profiles/76561198169337842#!/compare/1537488000/1537747200

Buyer: https://backpack.tf/profiles/76561198335791307#!/compare/1537401600/1537488000

https://backpack.tf/item/6275211423

https://i.imgur.com/pAYp9ew.png

We only see 10 ref, but given that it’s the correct amount of metal, it should be fine to assume that the sale is correct.

X = 6.5

Sale 4:

Sold to a bot for 6 keys + 12 ref

Seller: https://backpack.tf/profiles/76561198182591411#!/compare/1537488000/1537660800

Buyer: https://backpack.tf/profiles/76561198295122993#!/compare/1537574400/1537660800

https://backpack.tf/item/2860084869

https://i.imgur.com/pAYp9ew.png

X = 6.5

Other Sales:

https://backpack.tf/item/6275211423 (#1)

https://backpack.tf/item/3943889463 (#2 & #3)

https://backpack.tf/item/4853473963 (#4 & #5)

https://backpack.tf/item/3515977021 - not unusual at the time

https://backpack.tf/item/2695128606 - gambled

#1

Bulk for DBD Gauzed Gaze

https://backpack.tf/profiles/76561198011321852#!/compare/1536364800/1536451200

https://backpack.tf/profiles/76561198169337842#!/compare/1536364800/1536451200

#2

Untraceable

https://backpack.tf/profiles/76561198363395191#!/compare/1536969600/1537056000

https://backpack.tf/profiles/76561198128999327#!/compare/1536883200/1537401600 - might not be the buyer

#3

SCM

https://backpack.tf/profiles/76561198128999327#!/compare/1537401600/1537488000

https://backpack.tf/profiles/76561198182837799#!/compare/1537056000/1537401600

#4

Bulk for Miami Pullover

https://backpack.tf/profiles/76561198037248506#!/compare/1536364800/1536451200

https://backpack.tf/profiles/76561197994697258#!/compare/1536364800/1536451200

#5

Untraceable, buyer’s backpack hasn’t been scanned

https://backpack.tf/profiles/76561197994697258#!/compare/1536537600/1536710400

Sellers:

https://i.imgur.com/1GSoKxS.png

https://backpack.tf/item/6275211423 - 9 keys

https://backpack.tf/item/2829483059 - 9 keys

https://backpack.tf/item/5005225880 - ~9.52 keys

Sales at:

6.5 (2x)

9 (2x)

6.5 is a common trading point, and the 2 month unsold at 9 would suggest that a flat price of 9 would be too high.

Going with 6.5-9.