I checked the item histories and I couldn't find any sales for pure/items. However, I have a Marketplace.tf sale in date and one slightly out of date

Marketplace.tf sales: https://marketplace.tf/items/tf2/31024;5;u32

13/04/2020 (OUTDATED): $15 (median key price: $1.72, 15/1.72=8.72 keys)

18/06/2020: Sale at $14.99 (median key price: $1.98, 14.99/1.98=7.57 keys)

Seller at 7.33 keys (7.5 keys if rounded up)

Taking 7.57 keys as the possible value (7.5 keys if rounded up)