Great Hats on Fire.

https://backpack.tf/item/390277859

Sale 1) Sold for 71 Keys

https://backpack.tf/profiles/76561198079530619#!/compare/1508889600/1508976000

Low Outlier.

Sale 2) Sold for an It's a Puzzle to Me Prehistoric Pullover + 21 Keys

https://backpack.tf/profiles/76561198271428863#!/compare/1509753600/1509840000

http://www.tf2outpost.com/trade/29421773 - Capped by the Buyout of 100 Keys

Sale 3) Sold + Sunbeams Your Worst Nightmare + 60 Keys + Steaming Bonk Boy for a Nebula Universal Translator

https://backpack.tf/profiles/76561197961279983#!/compare/1510185600/1510272000 - Buyer's Backpack

Bulk sale.

Sale 4) Sold for 100 Keys

https://backpack.tf/profiles/76561197961279983#!/compare/1510444800/1510531200

Sale 5) Sold for 70 Keys?

https://backpack.tf/profiles/76561198072340223#!/compare/1512345600/1512432000

I asked the Seller and they said the trade was for 100 Keys but couldn't get a screenshot.

https://marketplace.tf/items/137;5;u14 - Sale at $199.99. Keys were ~$1.98 at the time.

199.99 / 1.98 = 101, which I'll round down to 100 Keys