Sale 1: (Untrace)

https://backpack.tf/item/7299379719

https://backpack.tf/profiles/76561198865210316#!/compare/1590019200/1590624000

https://backpack.tf/profiles/76561198872796421#!/compare/1590278400/1590364800

Sale 2: Marketplace.tf sale at 5.49 keys (Rounded to 5.5 keys)

https://backpack.tf/item/7291617564

https://marketplace.tf/items/tf2/1112;5;u3021

Sale on May 28 2020 at $10.49 (median key price: $1.91, 10.49/1.91=5.49 keys)

Sale 3: (Untrace)

https://backpack.tf/item/7265300260

https://backpack.tf/profiles/76561198280693486#!/compare/1590624000/1590537600

https://backpack.tf/profiles/76561198169936421#!/compare/1590537600/1590624000

Sale 4: Item deposit to Marketplace.tf

https://backpack.tf/item/7103171060

Sale 5: Sale at 5 keys 5 ref pure (rounded to 5 keys)

https://backpack.tf/item/4312255770

https://backpack.tf/profiles/76561198305676157#!/compare/1594936800/1595023200

Sale 6: Item deposit to Marketplace.tf

https://backpack.tf/item/2727240299

There's an unsold at 5.09 keys so 5.5 is too high.

Taking 5 keys flat as the value for my suggestion