Dropping a bit. There are a few sellers at 12 keys.

Classifieds at the time of posting:

4 x 12 keys

5 x 13 keys (2 x Specialized KS)

Sellers @ 12 keys:

http://www.tf2outpost.com/trade/22712443 - 1 week (Poorly bumped)

http://www.tf2outpost.com/trade/22898315 - 4 days (Auto bumped)

http://www.tf2outpost.com/trade/22907630 - 3 days (Auto bumped) x 2

Sellers @ 13 keys:

http://www.tf2outpost.com/trade/22682073 - 2 weeks

http://www.tf2outpost.com/trade/22864457 - 5 days

http://www.tf2outpost.com/trade/22903138 - 3 days (Specialized KS)

http://www.tf2outpost.com/trade/22924219 - 2 days

http://www.tf2outpost.com/trade/22943521 - 1 day (Specialized KS)

http://www.tf2outpost.com/trade/22936485 - 1 day

Very recently added:

http://www.tf2outpost.com/trade/22958518 - 12 keys

http://www.tf2outpost.com/trade/22951614 - 13 keys

http://www.tf2outpost.com/trade/22960183 - 13 keys

Most of the others have extras like Pro KS and are priced higher than 13 keys.