Bright Future

https://backpack.tf/item/454869213

Sale 1) ?

https://backpack.tf/profiles/76561197997268820#!/compare/1540684800/1540771200

https://backpack.tf/profiles/76561198813410945#!/compare/1540771200/1540857600

https://backpack.tf/item/4968787929

Sale 2) ?

https://backpack.tf/profiles/76561198040186479#!/compare/1545091200/1545264000

https://backpack.tf/item/337162841

Sale 3) Sold + 4 Keys + 20 Refined (~0.5 Keys) for a Green Energy Buckaroos Hat (28.5 Keys) + Duped Max's Severed Head (~19 Keys)

https://backpack.tf/profiles/76561197965158062#!/compare/1542758400/1542931200

https://backpack.tf/profiles/76561198071230830#!/compare/1542499200/1542931200

28.5 + 19 - 4 - 0.5 = 43 Keys

Buckaroos Mini

https://backpack.tf/suggestion/5c29b721cf6c75226576e1fd - 28.5 Keys

Sale 4) Sold + Killstreak Australium Wrench (~27 Keys) for an It's a Secret to Everybody Industrial Festivizer

https://backpack.tf/profiles/76561198071230830#!/compare/1543795200/1543968000

This would be better used to updated that Festivizer.

https://marketplace.tf/items/338;5;u17 - Sold for $87.99 when Keys were ~$1.78 each

https://marketplace.tf/items/5021;6/Mann%20Co.%20Supply%20Crate%20Key

87.99 / 1.78 = 49.43, which rounds to 49 Keys