Please hear me out! First suggestion :)

No price set for this yet, only two exist, and one on the market.

Previously, it was sold in this trade:

http://www.tf2outpost.com/trade/5918610

Description states 9-10 buds, current owner bought it for $300 (as shown in 6 main comment). 8 months ago, when the offer was stated, buds were 25-28 keys.

And now.. it is being resold for

http://www.tf2outpost.com/trade/11959684

It has been sitting for a month, auto bumped with Blue Status. 9 buds is his price.

Thought I might throw this in too. Maybe unreliable but goes with the ~9 buds price.

http://www.tf2pricecheck.net/Thread-PC-Stormy-13th-Hour-Triboniophorus-Tyrannus

Couldn't find any buyers for this hat and effect, sorry.

As a comparison to another hat with the same effect, the Brigade Helm is the closest Pyro-only hat in terms of Unusual prices. The Stormy 13th Hour Brigade Helm has a price of 7.4-9.2 buds. 9 is within this range.

Any feedback or suggestions are appreciated!