This is really a tough item to price. It's extremely rare, but it's so rare that nobody seems to know about it. The price range seems to be between 1 and 2 keys, but the 1 key ones are snatched up quickly, while the remainder are holding out for higher than 2 keys. Most trades with no b/o or a b/o that is halfway reasonable have been offered 1.5-3 keys, usually in items.

http://www.tf2outpost.com/trade/5600076, Sold for 1 key.

http://www.tf2outpost.com/trade/5636526, Sold for 2.66-3 (2 refined + scouts killed)

http://www.tf2outpost.com/trade/5614878, Sold for 5 refined.

http://www.tf2outpost.com/trade/5816578, offered 5.33 (same person from above), sold to someone else for unknown price

http://www.tf2outpost.com/trade/5631664, Unsold. Offered 1.5-2 keys in items twice.

http://www.tf2outpost.com/trade/5725280, Unsold. 1:1 with a Buildings Destroyed (conservatively 2 keys). 1 person agreed to it in comments.

http://www.tf2outpost.com/trade/5696393, Unsold. B/O 2 keys. Someone agreed to buyout

http://www.tf2outpost.com/trade/5860078, Unsold. B/O 1 key + 1.33 (only listed an hour)

http://www.tf2outpost.com/trade/5622327, Unsold. Offered 5.33. Also offered ~10 refined in items, but buyer quickly retracted.

We are more than halfway through the event, and these can only be obtained through the item drop system. Whether these become 1 reclaimed or 20 keys is dependent on if they stop dropping after Halloween.

http://stats.tf/item/6033/Strange_Part%3A_Halloween_Kills

When I say rare, I mean there are less than 50 in the game. I don't own one or have any plans to own one, but I don't understand why people are being so snide about it in the comments when this thing is going for the suggested price easily.