Using last month.

Sale 1:

Sold for 6 keys + 25 ref

Seller: https://backpack.tf/profiles/76561198311498888#!/compare/1542931200/1543017600

Buyer: https://backpack.tf/profiles/76561198148116943#!/compare/1543017600/1543104000

https://backpack.tf/item/7029329352

X = 6.5

Sale 2:

Sold for $9.50 on marketplace

https://marketplace.tf/items/1106;5;u3008

https://manic.tf/keyprice/?at=2018-11-25 - $9.5 / $1.73 = 5.49 keys

X = 5.5

Other Sales:

https://backpack.tf/item/6891138556 (#1)

https://backpack.tf/item/6779272078 - Not unusual at the time (shows up as a ~5.5 key purchase on bot.tf, seller doesn’t show in history)

https://backpack.tf/item/6402060203 - scrap

#1

Untraceable

https://backpack.tf/profiles/76561198313313803#!/compare/1542499200/1542758400

https://backpack.tf/profiles/76561198142600496#!/compare/1542585600/1542672000

Sellers:

https://i.imgur.com/Qpo3GAS.png

https://backpack.tf/item/6894572981 - ~6.7 keys

https://backpack.tf/item/6779272078 - 7 keys

https://backpack.tf/item/6775175971 - 7 keys

https://backpack.tf/item/6347645791 - ~8.35 keys

https://backpack.tf/item/2697999531 - 9 keys

Sales at:

5.5

6.5

Wasn’t gonna use 5.5, but 5.5 is supported by the (untraceable) bot.tf sale, so I’ll use it. That, and the buyers are still lower than what the sales actually were unrounded.

Going with 5.5-6.5.