Sale 1:

Sold for 10 keys

https://backpack.tf/profiles/76561198070497462#!/compare/1700784000/1700870400

https://backpack.tf/profiles/76561198263000084#!/compare/1694476800/1701734400

https://backpack.tf/item/5383030432

= 10 keys

Sale 2:

Sold for 6 keys + ~0.5 in metal

https://backpack.tf/profiles/76561199084784906#!/compare/1703376000/1703462400 - Near ID: 13961233538

https://backpack.tf/profiles/76561198064374638#!/compare/1703289600/1703721600 - All visible here

https://backpack.tf/item/12011314913

= 6.5 keys

Sale 3:

Sold for 3 keys + ~2.7 keys (at the time) in taunts + various other items/metal, adding up to ~6 keys total.

https://backpack.tf/profiles/76561199085116273#!/compare/1701216000/1701302400

https://backpack.tf/profiles/76561199096500582#!/compare/1701129600/1701302400

https://backpack.tf/item/9598452535

= 6 keys

Other Sales:

#1

https://backpack.tf/profiles/76561199159431326#!/compare/1700870400/1703289600

https://backpack.tf/profiles/76561199084784906#!/compare/1701993600/1702080000

https://backpack.tf/item/12011314913

Bulk

#2

https://backpack.tf/profiles/76561198858001037#!/compare/1700697600/1701129600

https://backpack.tf/profiles/76561199085116273#!/compare/1700870400/1700956800

https://backpack.tf/item/9598452535

Bulk for Prismatic Haze Table Tantrum + some metal

#3

https://backpack.tf/profiles/76561198131911699#!/compare/1702166400/1702598400

https://backpack.tf/profiles/76561198113190503#!/compare/1702512000/1702598400

https://backpack.tf/item/7469014032

Bulk for Cloud 9 Modest Pile of Hat

https://backpack.tf/item/11027423737 - scrap bot

https://backpack.tf/item/9955998495 - Mannco

Sellers:

https://imgur.com/a/9HsuVUy

https://backpack.tf/item/7469014032 - 12 keys

https://backpack.tf/item/9598452535 - ~13.6 keys

https://backpack.tf/item/10327665856 - 15 keys

https://backpack.tf/item/8340269192 - marketplace

Sales at:

6

6.5

10

As high as the sale at 10 may seem, there's nothing to suggest that it should be excluded. Going with a wide range here.

Taking 6-10.