Backpack.tf always keeps me busy and that's why I luv it :D

Note: For future purpose, I had rounded up keys to 6 ref. So, 1 ref = 0.1 keys, 2 ref = 0.3 keys, 3 ref = 0.5 keys, 4 ref = 0.7 keys and 5 ref = 0.9 keys.

Sellers:

Selling @ less than 2.8 keys:

http://www.tf2outpost.com/trade/13492616 - 2.3 keys

http://www.tf2outpost.com/trade/13539446 - 2.5 keys

http://www.tf2outpost.com/trade/12849814 - 2.5 keys

http://www.tf2outpost.com/trade/13496975 - 2.3 keys

http://www.tf2outpost.com/trade/13547221 - 2.5 keys

http://www.tf2outpost.com/trade/13461340 - 2.5 keys

http://www.tf2outpost.com/trade/13393305 - 2.5 keys

http://www.tf2outpost.com/trade/13351659 - 2.5 keys

Selling @ 2.8 keys:

http://www.tf2outpost.com/trade/13426231 - 5 days ago

http://www.tf2outpost.com/trade/13535460 - 1 day ago

No more in Outpost.

Since 2.5 keys has outnumbered them all, I assume that 2.5 keys is the price. Counter-proof or other typical suggestion for me are welcome. Good Luck and Happy Trading.