Resugg, and thanks to Eazy Peazy for input on my previous suggestion with more sales!

https://backpack.tf/item/10867348698

Purchased on SCM for $56.55 on Oct 30

https://gyazo.com/6c8e4810555884e239637b82328721d0

https://gyazo.com/d4be43191ff34753723960bd8e2050b4

Key prices

27th 2.15

28th 2.16

29th 2.13

30th 2.12

31st 2.10

1st 2.13

2nd 2.18

Avg 2.14

$56.55 / $2.14 = 26.4 keys, rounding to 26

Traded with sweets for items, approx 59 keys at the time

https://backpack.tf/profiles/76561198148471751#!/compare/1636070400/1636156800

https://backpack.tf/profiles/76561198068968841#!/compare/1636070400/1636243200

https://gyazo.com/eef3e0401545cf4fb185f03f470e1fb4

https://backpack.tf/item/10784518987

Auctioned on scrap.tf with a closing of 35 keys 3 ref, rounding to 35

https://scrap.tf/auctions/OJNZOX

others untraceable

https://backpack.tf/item/10781318656

untraceable

https://backpack.tf/item/10889765060

Sold for 35 pure

https://backpack.tf/profiles/76561198093248910#!/compare/1637366400/1637452800

https://backpack.tf/profiles/76561198115721685#!/compare/1637366400/1637539200

B/O was 35: https://gladiator.tf/listings/619965cb1577c06a978c5593

Sold for 38 pure

https://backpack.tf/profiles/76561198056666757#!/compare/1638489600/1638662400

https://backpack.tf/profiles/76561198115721685#!/compare/1638403200/1638489600

Sales from gladiator as supplementary evidence:

https://gladiator.tf/sales?item=Frantic%20Spooker%20Hat%20Outta%20Hell&at=2021-11-08T00:56:21.379Z

2 bought past 30 days:

1 @ 20 keys

1 @ 35 keys

New sales provided by Eazy Peazy:

https://backpack.tf/profiles/76561198040073503#!/compare/1643932800/1644019200

https://backpack.tf/profiles/76561198823527831#!/compare/1643932800/1644019200 - Sold for 68 keys

https://backpack.tf/profiles/76561198128279264#!/compare/1640736000/1640908800

https://backpack.tf/profiles/76561198040073503#!/compare/1640822400/1640908800 - Sold the day after it was tradeable to a buy order

https://backpack.tf/profiles/76561198894079927#!/compare/1641513600/1642550400 - Alt transfer

https://backpack.tf/profiles/76561199097845692#!/compare/1638748800/1638921600

https://backpack.tf/profiles/76561198894079927#!/compare/1639008000/1639699200 - Bulk

https://backpack.tf/profiles/76561198199244659#!/compare/1636502400/1636675200

https://backpack.tf/profiles/76561198045941055#!/compare/1636502400/1636588800 - Sold for 40 keys

https://backpack.tf/item/10784518987 https://marketplace.tf/items/tf2/31216;5;u202

$79.99 / $1.83 = 44 keys

https://mannco.store/item/440-frantic-spooker-unusual-hat-outta-hell

$120 / $1.65 = 73 keys

https://backpack.tf/profiles/76561198415325993#!/compare/1637020800/1641772800 - Untrace

Summary

20 (from gladiator)

26

35 (from gladiator)

35

35

38

40

44

59

68

73

Taking 35-44.

There are a lot of high sales, but with so many being around 35 then 44 seems like a reasonable high end, as Eazy Peazy said.