Gonna counter the current Suggestion with more sales.

Sale for Knifestorm Firewall (in-date at 375) + 100 keys pure = 475 keys

https://backpack.tf/profiles/76561198060730062#!/compare/1628640000/1628899200

https://backpack.tf/profiles/76561198124510043#!/compare/1628812800/1628899200

Sale for Steaming Antlers (in-date at 361) Seems low given he bought it for 475, maybe broken compare, will exclude for now until i got more info. Enlighten me, mods.

https://backpack.tf/profiles/76561198124510043#!/compare/1629072000/1629244800

https://backpack.tf/profiles/76561198040186479#!/compare/1629158400/1629244800

Mann co sale on Oct 16th https://mannco.store/item/440-darkblaze-unusual-attendant

$900 / $1.7 per key = 529 keys

Sold for 615 keys pure

https://backpack.tf/profiles/76561198126679929#!/compare/1634515200/1634601600

https://backpack.tf/profiles/76561198113466974#!/compare/1634428800/1634601600

Going with 475 - 615 keys.