Thank you to Shuffle Spy for helping out massively with this suggestion!

https://backpack.tf/profiles/76561198400462105#!/compare/1639267200/1639440000 - 26 keys

https://backpack.tf/profiles/76561199048815630#!/compare/1639440000/1639699200 - 26 keys

https://backpack.tf/profiles/76561198002920295#!/compare/1637280000/1638144000 - 20 Keys. Very low

https://backpack.tf/profiles/76561198140928358#!/compare/1637712000/1637971200 - 26 Keys

https://backpack.tf/profiles/76561198158179076#!/compare/1638489600/1638576000 - Added 2 Keys and ~1 Key of Items for a Max's Head (~28 Keys).

28 - 3 = 25

https://backpack.tf/profiles/76561199004803157#!/compare/1635379200/1635465600 - Untrace

https://backpack.tf/profiles/76561198841279602#!/compare/1634256000/1634342400 - Untrace

https://backpack.tf/profiles/76561198337734785#!/compare/1634688000/1634774400 - 25 Keys

https://backpack.tf/profiles/76561198957339086#!/compare/1638748800/1638835200 - 23 Keys + 24 Refined to a buy order. Probably won't consider.

https://backpack.tf/profiles/76561198453530349#!/compare/1638835200/1638921600 - Untrace

https://backpack.tf/profiles/76561198188093413#!/compare/1632614400/1632700800 - Untrace

https://backpack.tf/profiles/76561198795826430#!/compare/1634169600/1634256000 - Untrace

https://backpack.tf/profiles/76561198315344580#!/compare/1634342400/1635552000 - Untrace

https://backpack.tf/profiles/76561198850178158#!/compare/1636070400/1636156800 - Untrace

https://backpack.tf/item/6849809741 - Everything else in this history is a series of bot purchases and dumps to further bots

https://marketplace.tf/items/tf2/30977;5;u57 - Sold for $53.99 twice (29 Keys) and $65 twice (34 and 36 Keys)

https://gladiator.tf/listings/61b5c759b6067647b05659c8 - Given there was a seller at 26 Keys when the sale at 36 Keys happened, 36 is too high

Additionally, 34 looks to be too high with the multiple sales for less (the two sales at 29 were within 9 days of the sale at 34).

Sales

20, 23, 25, 25, 26, 26, 26, 29, 29, 34, 36

As suggested by Shuffle Spy, 25 to 29 would work as a range.

Listings

One listed at 65 USD on marketplace -> 65/1.83 = 35.52 ≈ 36 - High considering sale range