Resuggestion, thanks to Xerogyf for the info!

Challenge 19, Team F.L.A.M.B.E.S!

79th suggestion, made by Beaser!

https://marketplace.tf/items/tf2/627;5;u7 - $49.99 / $1.89 = 26.45 keys

https://backpack.tf/item/942343727

Sale #1 -

Untrace?

https://backpack.tf/profiles/76561198972047944#!/compare/1588118400/1588723200

https://backpack.tf/profiles/76561198026926990#!/compare/1588118400/1588377600

Rest of the sales are gambles, taking 26 flat!

Revised Sales:

Sale 1:

https://backpack.tf/profiles/76561198972047944#!/compare/1588118400/1588723200

https://backpack.tf/profiles/76561198026926990#!/compare/1588118400/1588377600

untrace

sale 2:

https://backpack.tf/profiles/76561198067917465#!/compare/1592006400/1592092800

https://backpack.tf/profiles/76561198279539667#!/compare/1591747200/1592092800

https://backpack.tf/profiles/76561198026526425#!/compare/1592006400/1592092800

Untrace

sale 3:

https://backpack.tf/profiles/76561198026526425#!/compare/1592611200/1592697600

https://backpack.tf/profiles/76561198118157202#!/compare/1592611200/1592697600

https://backpack.tf/profiles/76561198030214998#!/compare/1592611200/1592697600

https://backpack.tf/profiles/76561198850274253#!/compare/1592697600/1592784000

Untrace / bulk

sale 4:

https://marketplace.tf/items/tf2/627;5;u7

$49.99 / $1.89 = 26.45 keys

https://backpack.tf/item/942343727

Xerogyf's Part:

https://mannco.store/item/15374

https://mannco.store/item/1

$42.49 / $1.90 = 22.36 keys

Taking 22 - 26 keys

Note seller at ~20 keys