Don't even know why I closed the suggestion. I apologise.

(2 on outpost, can't track the first one)

http://www.tf2outpost.com/trade/17918782 - bought for a bud = 20keys

http://www.tf2outpost.com/trade/17978425 - sold for 16 keys (quicksell)

http://www.tf2outpost.com/trade/18006458 - sold for Orb Fire Jeepcap

http://www.tf2outpost.com/trade/17929790 ~20keys

EXTRA

(Read this, Radiated Banana)

Why 2nd link was actually sold for 16 keys

In the item history, Seamus appears to have sold the hat to Parmesan Chicken. Hence, the keys should be in his backpack.

But the only thing of value in his backpack is a Steaming Company Man, last seen with NecroTed.

If we look at NecroTed's backpack http://www.tf2outpost.com/backpack/76561198044387084

On the page where there are 3 buds and 47 keys, if you examine the last key on the second row, the history states that it was with Chicken, then Seamus.

Therefore, we can conclude that the hat in question was quicksold for 16 keys (or less) to Parmesan Chicken.