So easy to get one of this for 12 keys:

Selling for 11 keys:

http://www.tf2outpost.com/trade/10147878

Currently selling for 12 keys :

http://www.tf2outpost.com/trade/9726351 (13 because its already wrapped, sold 1)

http://www.tf2outpost.com/trade/10183893 (13 because its his wrap)

http://www.tf2outpost.com/trade/10112336 (3 days)

http://www.tf2outpost.com/trade/10112351 (4 days)

http://www.tf2outpost.com/trade/10172758 (13, wrapped)

http://www.tf2outpost.com/trade/9438064 (13, wrapped)

http://www.tf2outpost.com/trade/10189728 (13, wrapped)

http://www.tf2outpost.com/trade/10157718 (13, wrapped)

http://backpack.tf/classifieds/search/333/6/0 (there's 1 for 12 keys)

Unsold at 13 keys:

http://www.tf2outpost.com/trade/9780341 (2 weeks)

http://www.tf2outpost.com/trade/10172410 (1 day)

Buyer trade:

http://www.tf2outpost.com/trade/9930115 (2 offers of 11 keys (wrapped), note he didn't even state a price)

Could've place a range of 11-12 keys, but insufficient proof as for now.