August 7, 2020 at $75.99

$75.99 / $1.85 = 41.08 keys

https://backpack.tf/item/5841880624 (assuming its this one and owner didn't refresh their backpack until the 2nd)

~~~~~

October 3, 2020 at $64

$64 / $1.85 = 34.59 keys

https://backpack.tf/item/9132233414

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October 4, 2020 at $64

$64 / $1.85 = 34.59 keys

https://backpack.tf/item/7707714053

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October 13, 2020 at $75

$75 / $1.89 = 39.68 keys

https://backpack.tf/item/6347239547

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https://marketplace.tf/items/tf2/30833;5;u16

Sales at 41, 35, 35, 40.

Classified seller at 40 keys has already sold on marketplace, the seller has just not refreshed their marketplace inventory.

Taking 35-41