Credit to K1ng! I finished my Triple CPS Engi set! Thanks again for the trade, Hander1!

Sale 1)

~20 keys, way above previous B/Os

https://marketplace.tf/items/tf2/399;5;u18

Sale 2)

Untraceable, B/O was 12 keys

https://backpack.tf/profiles/76561198024978576#!/compare/1688342400/1689897600

https://backpack.tf/profiles/76561198124535450#!/compare/1686441600/1687132800

https://next.backpack.tf/classifieds/snapshots/Circling%20Peace%20Sign%20Ol'%20Geezer/64acba07c54dcaeed002fe13

~12 keys

Sale 3)

https://backpack.tf/profiles/76561198121520551#!/compare/1687824000/1689120000

https://backpack.tf/profiles/76561199085308746#!/compare/1688947200/1689033600

https://next.backpack.tf/classifieds/snapshots/Circling%20Peace%20Sign%20Ol'%20Geezer/64acba07c54dcaeed002fe13

Sale 4)

Item History: https://backpack.tf/item/6508428668

Buyer: https://backpack.tf/profiles/76561198064724507#!/compare/1690329600/1690502400

Sold for an Australium Black Box(recently priced at 14.1 keys), and 33 refined metal (11 Craft Hats were instantly crafted with the 33 metal = 0.3 keys) ---14.1 - 0.3 = 13.8 keys = ~ 14 keys.

Going with a range of 12 - 14 keys or an average of 13 keys.

Feedback welcome!