Using sales from August onwards, due to lack of stable sales.

Sale 1:

Sold for 30 keys

Seller: https://backpack.tf/profiles/76561198164651434#!/compare/1535414400/1535500800

Buyer: https://backpack.tf/profiles/76561198046943416#!/compare/1534982400/1535414400

https://backpack.tf/item/2216906948

X = 30

Sale 2:

Sold for 25 keys

Seller: https://backpack.tf/profiles/76561198058834083#!/compare/1534118400/1534204800

Buyer: https://backpack.tf/profiles/76561198165663774#!/compare/1534118400/1536624000

https://backpack.tf/item/5136956675

X = 25

Sale 3:

Sold for $23 on marketplace.tf

https://marketplace.tf/items/463;5;u3001

http://manic.tf/keyprice/?at=2018-08-18 - $42.99 / $1.89 = 22.75 keys

Couldn’t find item history.

X = 23

Sale 4:

Sold for 18 keys

Seller: https://backpack.tf/profiles/76561198008388703#!/compare/1534204800/1534291200

Buyer: https://backpack.tf/profiles/76561198079413347#!/compare/1534204800/1534291200

https://backpack.tf/item/6171599577

X = 18

Sale 5:

Sold to a bot for 17 keys

Seller: https://backpack.tf/profiles/76561198046943416#!/compare/1535500800/1536019200

Buyer: https://backpack.tf/profiles/76561198334598690#!/compare/1535846400/1535932800

https://backpack.tf/item/2216906948

https://i.imgur.com/llGzn46.png - labelled as 17 keys + 4.66 ref. If ref really was involved, it wouldn’t affect the value of this sale.

X = 17

Other Sales:

https://backpack.tf/item/2216906948 (#1)

https://backpack.tf/item/6253148303 (#2)

https://backpack.tf/item/6982218331 (#3 & #4)

https://backpack.tf/item/927273592 - tradeit and swap bots

https://backpack.tf/item/6763449478 - mannco stuff

https://backpack.tf/item/5915692920 - scammer stuff

#1

Untraceable

https://backpack.tf/profiles/76561198334598690#!/compare/1536364800/1536451200

https://backpack.tf/profiles/76561198056782115#!/compare/1535673600/1536451200

https://i.imgur.com/llGzn46.png - labelled as 28 keys

#2

Gambled/scammed/transferred to alt/friend.

https://backpack.tf/profiles/76561198064788088#!/compare/1534723200/1534809600

https://backpack.tf/profiles/76561198836017448

#3

Untraceable, appears to be bulk

https://backpack.tf/profiles/76561198038825523

https://backpack.tf/profiles/76561198081172172#!/compare/1533859200/1533945600

#4

Untraceable

https://backpack.tf/profiles/76561198081172172#!/compare/1533859200/1533945600

https://backpack.tf/profiles/76561198153360103#!/compare/1534550400/1534636800

Sellers:

https://i.imgur.com/tlXBQE8.png

https://backpack.tf/item/6352847653 - 30 keys

https://backpack.tf/item/5136956675 - 110 keys

Sales at:

17

18

23

25

30

Excluding 17 and 18 as they are either at, or near buy order prices, and would create a dumb range if used here.

Going with 23-30.