2 month old price, needs a bump. There are honestly very few on the market, with 1 link having a few offers, another link having no offers, and the third link being a special duped set. But people rejected 11 key offers constantly, and also 12 keys as well. This implies that they're looking for more, and honestly, it's not hard to wait a while to get 13 keys for any unusual.

http://www.tf2outpost.com/trade/11378402

refuses offer of 12 keys

http://www.tf2outpost.com/trade/11687759

rejected offer of 12 keys

http://www.tf2outpost.com/trade/10655569

offer of about 13 keys in items [rejected]