resuggestion from here: https://backpack.tf/suggestion/5f13907d449ceb5bb2455dfc#comment-5f3c9d0a9a178a78ad0df9ed

summary of relevant sales:

Sale #1

seller: https://backpack.tf/profiles/76561198073896407#!/compare/1590192000/1590364800

buyer: https://backpack.tf/profiles/76561198036469000#!/compare/1590105600/1590192000

Sold for 25 keys.

Sale #2

seller: https://backpack.tf/profiles/76561198205723668#!/compare/1591660800/1591747200

buyer: https://backpack.tf/profiles/76561198113971364#!/compare/1591660800/1591747200

Sold for Collector's Professional Killstreak Machina + 2 keys = 28 keys

Mini for Machina by Avatar Shuffle Spy (cheers m8!) :

https://marketplace.tf/items/tf2/526;14;kt-3 - $55.55 (29 Keys), $44.55 (24 Keys), and $40 (22 Keys)

https://steamcommunity.com/market/listings/440/Collector%27s%20Professional%20Killstreak%20Machina - Sold for $32.55 (low), $69.98 (28 Keys), $71.01 (29 Keys), and $131.16 (high)

22 - 29 averages to 25.5, which will make sale #2 ~28 Keys.

Sale #3

seller: https://backpack.tf/profiles/76561198113971364#!/compare/1592006400/1592092800

buyer: https://backpack.tf/profiles/76561198359982620#!/compare/1592006400/1592524800

Sold for Green Energy Backbiter's Billycock = 31 keys.

Resold for 12 keys: https://backpack.tf/profiles/76561198359982620#!/compare/1597017600/1597104000

Going with 25-28 keys.