Without a doubt, this is one of the most badass cosmetic in the whole of TF2.

Classified ads at the time of posting:

http://m.imgur.com/PNEAq63

http://backpack.tf/classifieds?item=Doublecross-Comm&quality=1&tradable=1&craftable=1

1 buy order at 3.37 keys

1 buy order at 3.21 keys

3 buy orders at 3.19 keys

Sale at 3 keys and 6 refined: (Credits to B>Earbuds, Keys, | trade.tf)

http://m.imgur.com/kwYrDgr

Buyer at 3 keys and 4 refined (~3.25 keys):

http://www.tf2outpost.com/trade/26943767 (~1 month old)

Buyer at 3 keys and 3.33 refined (~3.2 keys):

http://www.tf2outpost.com/trade/27048503 (~3 weeks old)

Buyer at 3 keys and 3.22 refined (~3.2 keys):

http://www.tf2outpost.com/trade/27170567 (~6 days old, never bumped)

Buyers at 3 keys and 3 refined (~3.2 keys):

http://www.tf2outpost.com/trade/26804829 (~2 months old)

http://www.tf2outpost.com/trade/25627782 (~6 months old)

This is all I could find on Outpost that are valid at the time of posting this suggestion.