Mini.

Sale 1: https://backpack.tf/profiles/76561198163650366#!/compare/1575072000/1575244800

https://backpack.tf/profiles/76561198120672630#!/compare/1575072000/1575158400

?

Sale 2: https://backpack.tf/profiles/76561198120672630#!/compare/1575072000/1575158400

https://backpack.tf/profiles/76561198049053401#!/compare/1555718400/1575158400

?

Sale 3: https://backpack.tf/profiles/76561198376331369#!/compare/1575590400/1575676800

https://backpack.tf/profiles/76561198304602112#!/compare/1575504000/1575676800

It would appear to be 8 keys + sum ref.

Sale 4: https://backpack.tf/profiles/76561198304602112#!/compare/1575676800/1575763200

https://backpack.tf/profiles/76561198002757046#!/compare/1575676800/1575763200

Qs.

Sale 5: https://backpack.tf/profiles/76561198002757046#!/compare/1576022400/1576108800

https://backpack.tf/profiles/76561198145314530#!/compare/1576108800/1576195200

?

Sale 6: https://backpack.tf/profiles/76561198286543973#!/compare/1572912000/1573084800

https://backpack.tf/profiles/76561198044684270#!/compare/1572998400/1573084800

Qs.

Sale 7: https://backpack.tf/profiles/76561198117090444#!/compare/1572220800/1572480000

https://backpack.tf/profiles/76561198161586384#!/compare/1572393600/1572480000

?

Sale 8: https://backpack.tf/profiles/76561198161586384#!/compare/1572480000/1572566400

https://backpack.tf/profiles/76561198401731069#!/compare/1572480000/1572566400

It would appear, that it sold for 7 keys + sum ref

Sale 9: https://backpack.tf/profiles/76561198401731069#!/compare/1572480000/1572566400

https://backpack.tf/profiles/76561198403329558#!/compare/1572480000/1572566400

Sold for 8 keys + .4 in ref = 8.4

Sale 10: https://backpack.tf/profiles/76561198403329558#!/compare/1572566400/1572652800

https://backpack.tf/profiles/76561198024999234#!/compare/1572566400/1572652800

Sold for a Kill-a-Watt Frenchman's Beret (10.5 keys), taking 11.

Mini for the Beret: https://backpack.tf/suggestion/5e07d2c8def5f4554060ca17

Sale 11: https://backpack.tf/profiles/76561198024999234#!/compare/1572739200/1572825600

https://backpack.tf/profiles/76561198941221728#!/compare/1572652800/1572825600

Use on the Ushanka.

Sale 12: https://marketplace.tf/items/tf2/436;5;u62 - 17/1.80 = ~9.5

Sale 13: https://marketplace.tf/items/tf2/436;5;u62 - 21.99/1.72 = ~13

Sales: 8, 7, 8.5, 11, 9.5 and 13. Classies: https://i.imgur.com/OSOEQUR.png. Going with 8-11.