Resubmitting due to things Cobalt and Julia pointed out.

Sale #1

Sold along with 2 keys of sweets for a Blizzardy Storm Magistrate's Mullet (16 keys)

http://backpack.tf/profiles/76561198060578721?time=1430550000

http://backpack.tf/profiles/76561198060578721?time=1430636400

With overpay, this makes the Stormy Storm Scotch Bonnet worth approx. 12 keys

Sale #2 (seems to be an outlier - not using)

Sold for 10 keys

http://backpack.tf/profiles/76561198095576590?time=1425024000

http://backpack.tf/profiles/76561198095576590?time=1425110400

Sale #3 (This one's a bit of a stretch given how long ago it was, but it is necessary in order to determine outliers)

Sold for a Bubbling Tartan Tyrolean (15 keys)

http://backpack.tf/profiles/76561198066594317?time=1422086400

http://backpack.tf/profiles/76561198066594317?time=1422950400

With overpay, this sale values the Bonnet at approx. 14 keys

==Mini==

Blizzardy Storm Magistrate's Mullet

Sold with about 1 key of sweets for a Bubbling Familiar Fez (17 keys)

Seller before: http://backpack.tf/profiles/76561198057528425?time=1423296000

Seller after: http://backpack.tf/profiles/76561198057528425?time=1423900800

Blizzardy Storm Magistrate's Mullet History: http://backpack.tf/item/853180751

Bubbling Familiar Fez History: http://backpack.tf/item/822591857

Bubbling Familiar Fez

Sold along with 2 keys of sweets for a Spec. Australium Grenade Launcher ( 19 keys)

Seller before: http://backpack.tf/profiles/76561198054245996?time=1428303600

Seller after: http://backpack.tf/profiles/76561198054245996?time=1428390000

Spec. Australium Grenade Launcher History: http://backpack.tf/item/2208603529

Bubbling Familiar Fez History: http://backpack.tf/item/822591857

That's all I could find... please let me know if I missed anything.