Using last 2 months, due to lack of sales in the last month.

Sales 1 & 2:

Sold for $46.67 & $49.99

https://marketplace.tf/items/30816;5;u3014

https://manic.tf/keyprice/?at=2018-08-26 - $46.67 / $1.89 = 24.69 keys

https://manic.tf/keyprice/?at=2018-08-31 - $49.99 / $1.88 = 26.59 keys

X = 27

X = 25

Can’t trace the exact histories, but here are a few that were on marketplace at the time:

https://backpack.tf/item/5221950420

https://backpack.tf/item/5184971084

Sale 3:

Quicksold with some ref for 18 keys

Seller: https://backpack.tf/profiles/76561198167988237#!/compare/1535587200/1535673600

Buyer: https://backpack.tf/profiles/76561198107900967#!/compare/1535587200/1535673600

https://backpack.tf/item/5184874782

X = 18

Other Sales:

#1

Untraceable

https://backpack.tf/profiles/76561198064490192#!/compare/1535587200/1535760000

https://backpack.tf/profiles/76561198167988237#!/compare/1535587200/1535673600

Might even be the one that sold on marketplace

#2

Untraceable

https://backpack.tf/profiles/76561198107900967#!/compare/1535760000/1535846400

https://backpack.tf/profiles/76561198218497692#!/compare/1535846400/1535932800

#3

Untraceable

https://backpack.tf/profiles/76561198218497692#!/compare/1536278400/1536364800

https://backpack.tf/profiles/76561198050359148#!/compare/1504569600/1536796800

Sellers:

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

https://backpack.tf/item/5190647969 - 65 keys

https://backpack.tf/item/5564811740 - 70 keys

And another one on scrap for a fair bit higher than the sales we have.

Sales at:

18

25

27

18 quicksold, and already appears to be an outlier. Excluding 18.

Going with 25-27.