This was a fun one. Re-suggesting from https://backpack.tf/suggestion/620440e2de3d4452016bdd56#comment-624f81e49e3fca386a09df01.

Bought for 30 keys

https://backpacktf.trade/profiles/76561198046353418#!/compare/1644278400/1644364800

Seller:

https://backpack.tf/profiles/76561198382742004#!/compare/1645833600/1645920000

Buyer:

https://backpack.tf/profiles/76561199102777012#!/compare/1645833600/1645920000

Untraceable. Looks like the seller sold for keys and then bought https://backpack.tf/item/7291103508 specialized killstreak australium sniper rifle but hard to know for sure.

New sales:

https://backpack.tf/profiles/76561199102777012#!/compare/1647734400/1647993600

https://backpack.tf/profiles/76561198090261302#!/compare/1647648000/1647734400

https://backpack.tf/profiles/76561198090261302#!/compare/1647648000/1647734400 - It looks like the Dragonborn sold for 95 keys, 50 remain in the compare, so "45" was spent on the Skullbrero. That being said, it seems it was actually 42 https://gladiator.tf/sales?item=Abyssal%20Aura%20Skullbrero&at=2022-04-08T00:22:59.289Z (I'm guessing some keys went to the killstreak kit)

https://backpack.tf/profiles/76561198212497608#!/compare/1648944000/1649030400 - Sold for 18 keys, low so I doubt that's the whole sale

https://backpack.tf/profiles/76561198280209340#!/compare/1648771200/1649030400

https://backpack.tf/profiles/76561198212497608#!/compare/1648684800/1648771200 - Better used on the Prancer's

https://backpack.tf/profiles/76561198203207940#!/compare/1648598400/1648684800

https://backpack.tf/profiles/76561198280209340#!/compare/1648598400/1648684800 - Sold for 32 keys + Kit (minor)

https://marketplace.tf/items/tf2/31066;5;u125

$66.67 / $1.78 = 37 keys.

Going with 32-37 as recommended by https://backpack.tf/u/76561198195734346