Finally getting round to this. My purchase of the SFB Hong Kong Cone on December 3rd 2024 is the only in-date sale of this beauty. After a lot of negotiation, Kolt and I eventually settled on $3700 via marketplace.tf.

Proof

Price I bought it for: $3700 on marketplace.tf on December 3rd 2024 from Kolt

The sale is viewable on marketplace here: https://marketplace.tf/items/tf2/30177;5;u83

Or a screenshot here: https://imgur.com/a/SLRtiBr

Further proof of the $3700 purchase from my marketplace orders page: https://imgur.com/a/CxNNpdv

Average key price on marketplace.tf on December 3rd 2024: $1.76

Average key prices are viewable on marketplace here: https://marketplace.tf/items/tf2/5021;6

Or a screenshot here: https://imgur.com/a/mAKgUZ4

3700 / 1.76 = 2102.27 keys

According to the pinned "Rules for Unusual Price Suggestions" on the backpack forums, because this hat is valued over 1000 keys it should be rounded to the nearest 50 keys.

2102.27 rounded to the nearest 50 keys = 2100 keys

Thanks!