This is my first suggestion

credit to The Nameless One and Spu_

thank you for your information

sold for 1 key+ 3 ref

http://bazaar.tf/trade/757492 (not in his backpack. i assume he sold that)

sold for 1 key + 4 ref

http://www.tf2outpost.com/trade/22108519

sold for 2 keys

http://i.imgur.com/vy9FZb2.png

2 keys offer but declined

http://www.tf2outpost.com/trade/21992565 declined 1 key + strange sandvich safe (7 ref)

sold for 2 keys

http://www.tf2outpost.com/trade/22010718

there are only6-7 sellers on the market and they are selling this for 3 keys or above. Therefore, i think this is more than enough