Item 1:

https://backpack.tf/item/3930221323

Sale 1:

https://backpack.tf/profiles/76561198177872379#!/compare/1770768000/1770854400

https://backpack.tf/profiles/76561198850313548#!/compare/1770768000/1770854400

Sold for 28 keys pure (ID 16715804460)

Sale 2:

https://backpack.tf/profiles/76561199185890046#!/compare/1769385600/1769472000

https://backpack.tf/profiles/76561198177872379#!/compare/1769385600/1769472000

Bulk, inventory sale

Sale 3:

https://backpack.tf/profiles/76561198151389427#!/compare/1764288000/1764720000

https://backpack.tf/profiles/76561199185890046#!/compare/1764201600/1764460800

Sold for Taunt: The Drunken Sailor (1) + 23 keys (ID 16463597819)

= 24

Sale 4:

https://backpack.tf/profiles/76561199026390261#!/compare/1764115200/1764201600

https://backpack.tf/profiles/76561198151389427#!/compare/1764028800/1764201600

Only 13 keys match (ID 16443004601)

//

Sellers:

BPTF - None (ender's sold)

MPTF - https://marketplace.tf/items/tf2/30616;5;u3132 - None

STN - https://stntrading.eu/item/tf2/Unusual+Galactic+Connection+Taunt%3A+The+Proletariat+Posedown - None

SCM - https://steamcommunity.com/market/listings/440/Unusual%20Taunt%3A%20The%20Proletariat%20Posedown?filter=Galactic+Connection - None

Sale(s):

24, 28, 13

Considering 13 keys an outlier as there may have been something missing plus other two sales suggest higher especially since it was bought for 24~ keys only 2 days later.

Going with 24 - 28 keys