Sale 1:

Sold for $14 on marketplace.tf

https://marketplace.tf/items/30843;5;u3010

http://manic.tf/keyprice/?at=2018-08-25 - $14 / $1.9 = 7.37 keys

Couldn't find item history.

X = 7.5

Sale 2:

Sold for 5 keys + 20 ref

Seller: https://backpack.tf/profiles/76561198335791307#!/compare/1536451200/1536537600

Buyer: https://backpack.tf/profiles/76561198435055904#!/compare/1536364800/1536537600

https://backpack.tf/item/6266362701

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

X = 5.5

Sale 3:

Sold to a bot for 3 keys + 22 ref?

Seller: https://backpack.tf/profiles/76561198140076265#!/compare/1536969600/1537228800

Buyer: https://backpack.tf/profiles/76561198334598690#!/compare/1536883200/1536969600

https://backpack.tf/item/7030127307

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

Compare shows 3 keys + 9 ref, which would also round to 3.5.

X = 3.5

Other Sales:

https://backpack.tf/item/6266362701 (#1)

https://backpack.tf/item/6912870848 - tradeit and scammers

https://backpack.tf/item/6489434953 - tf2mart stuff

#1

https://backpack.tf/profiles/76561198435055904#!/compare/1536624000/1537056000

https://backpack.tf/profiles/76561198199330914#!/compare/1536537600/1536624000

Sellers:

https://i.imgur.com/QSR5tir.png

https://backpack.tf/item/7030127307 - 5.56 keys

https://backpack.tf/item/6666462808 - 7 keys

Sales at:

3.5

5.5

7.5

7.5 is too high given the 4 month unsold at 7. Excluding 7.5.

3.5 is too low given the 3 buyers at 4+ keys https://i.imgur.com/vNBAij9.png

Going with 5.5 flat.