This is a counter, some older sales may be grandfathered in.

Sale 1:

Sold for 24 keys

https://backpack.tf/profiles/76561198850274253#!/compare/1760659200/1760745600

https://backpack.tf/profiles/76561199853690889#!/compare/1760659200/1760745600

https://backpack.tf/item/7959087649

= 24 keys

Sale 2: - Credit to Shuffle/Mindacos/Clone

Sold to a bot for 22 keys + just over half a key in metal

https://backpack.tf/profiles/76561199663649981#!/compare/1757030400/1757203200 - Near ID: 16144190897

https://backpack.tf/profiles/76561198350712076#!/compare/1757030400/1757203200

https://backpack.tf/item/8001114333

https://imgur.com/a/EyhvQq6

= 23 keys

Sale 3:

Most likely sold for 16 keys

https://backpack.tf/profiles/76561198325696105#!/compare/1756598400/1756684800

https://backpack.tf/profiles/76561199853690889#!/compare/1756598400/1756684800

https://backpack.tf/item/8001114333

= 16 keys

Other Sales:

#1

https://backpack.tf/profiles/76561199853690889#!/compare/1756598400/1756684800

https://backpack.tf/profiles/76561199663649981#!/compare/1756598400/1756684800

https://backpack.tf/item/8001114333

Untraceable

#2

https://backpack.tf/profiles/76561199034664938#!/compare/1756684800/1757808000

https://backpack.tf/profiles/76561199110809353#!/compare/1757203200/1757289600

https://backpack.tf/item/7959087649

Untraceable, 4 keys and a cheap cosmetic match

#3

https://backpack.tf/profiles/76561199853690889#!/compare/1760745600/1760832000

https://backpack.tf/profiles/76561198084813853#!/compare/1758153600/1760918400

https://backpack.tf/item/7959087649

Untraceable

#4

https://backpack.tf/profiles/76561198084813853#!/compare/1760918400/1761091200

https://backpack.tf/profiles/76561198850178158#!/compare/1760832000/1760918400

https://backpack.tf/item/7959087649

Untraceable, some metal matches

Sellers:

https://i.imgur.com/VDsEuko.png

https://backpack.tf/item/7959087649 - ~22.5 keys

https://backpack.tf/item/14277684901 - 28 keys

https://stntrading.eu/item/tf2/Unusual+Searing+Plasma+Bottle+Cap

https://backpack.tf/item/8001114333

https://i.imgur.com/t2pJSXY.png - ~23.5 keys

Sales at:

16

23

24

Taking Minda’s advice on excluding the potential 16 sale as a buy order dump.

The seller at ~22.5 would actually round down with a more accurate key price:

https://i.imgur.com/o0S5emb.png

Using the seller as the low-end. The 23 sale is pretty close to 22 anyway,

Taking 22-24 keys.