One sale for 18 keys. Multiple rejected offers of 16-16.75 keys. Can't really buy this for under 18 any more.

ACTUAL SALES

17.5 keys - http://www.tf2outpost.com/trade/10267365 - sold for white bills + 8 keys - http://i.imgur.com/AQZsPaI.jpg (thanks to moshspeggeti)

http://www.tf2outpost.com/trade/9614852 - this is >1 month old, but I'll use this to set the low end for now.

CURRENT TRADES

http://www.tf2outpost.com/trade/10406025

Best Offers:

1 buds? - http://www.tf2outpost.com/trade/9735235

16 keys, twice – once on current trade and once here - http://www.tf2outpost.com/trade/9735235

15 keys

http://www.tf2outpost.com/trade/10072079

Best Offers:

16.75 keys