I think it's finally time for this hat to get a price tag. Couldn't trace any other sales apart from the ones on mannco.store. Three happened in total:

Proof of key values and hat sales taken from mannco.store: https://imgur.com/a/gHrmXhN

The image is divided into three sections, based on each sale. On top, there's the average price of keys on that day and at the bottom is the price the hat got sold at. (For better readability, open image in new tab)

For verifying the screenshots I'll leave the original page links:

Hat history link: https://mannco.store/item/440-something-burning-this-way-comes-unusual-tough-guy-s-toque

Key history link: https://mannco.store/item/440-mann-co-supply-crate-key

2026-01-05: 1050$, key average price 1.71$ => 1050/1.71 = 614 keys

2026-02-26: 1249.99$, key average price 1.77$ => 1249.99/1.77 = 706 keys

2026-04-08: 1500$, key average price 1.84$ => 1500/1.84 = 815 keys.

614 + 706 + 815 = 2135 / 3 = 711.6666 keys.

I doubt the price will actually go down, so I feel like using only the high value would be justified and good enough for this hat and effect. However, since these happened basically back to back on an OG halloween effect (within a month or two), where many of these don't change hands for multiple years, I'll stick to a range of 614-815 keys, which will average out at 714 keys.