The Caribou suggestion was closed. Its current in-date sales are...

https://marketplace.tf/items/tf2/30974;5;u127 - $140 (83 Keys)

https://backpack.tf/profiles/76561198156255538#!/compare/1586304000/1586390400 - Added 12 Keys for a GBH Tree (98 Keys)

https://backpack.tf/profiles/76561198195784087#!/compare/1586390400/1586476800 - Burning Beenie (use there)

83 - 86 will work for the Caribou.

The Tree's sales...

https://backpack.tf/profiles/76561198160856661#!/compare/1584144000/1584230400 - Caps at the buyout of 100 Keys

https://imgur.com/a/e2QDKkb - Buyout of 100 Keys

https://backpack.tf/profiles/76561198063029136#!/compare/1584316800/1584403200 - No sales for the Western, so exclude this sale

https://backpack.tf/profiles/76561198170190173#!/compare/1585094400/1585180800 - PE Whirly (93.5 Keys) + 2 Keys

Taking 96 - 100 Keys for the Tree, which averages to 98 Keys

The Whirly's sales...

https://backpack.tf/profiles/76561198150917840#!/compare/1584921600/1585008000 - 87 Keys

https://backpack.tf/profiles/76561198280434589#!/compare/1586131200/1586217600 - Bulk sale, exclude

https://backpack.tf/profiles/76561197995029705#!/compare/1586304000/1586390400 - ?

https://backpack.tf/profiles/76561198067390585#!/compare/1586131200/1586908800 - ?

https://backpack.tf/profiles/76561198067390585#!/compare/1587686400/1592092800 - Bulk sale

https://backpack.tf/profiles/76561198170190173#!/compare/1591488000/1591574400 - 93 Keys

https://backpack.tf/profiles/76561198305494036#!/compare/1591488000/1591574400 - 100 Keys

Taking 87 - 100 Keys for the Whirly, which averages to 93.5 Keys

Since you're selling this for 75 Keys, 75 - 85 will work, since the Caribou is now 84.5, which rounds to 85 Keys.