Another sale happened recently, taking all proof from the previous suggestion and adding 1 more. (redoing it because used wrong bud value and messed up my highend)

Sale #1

http://www.tf2outpost.com/trade/21367287

Sold for 23 keys pure + 1 key in sweets (Current owner told me in chat) ~ 24 keys = 1.3 buds

Sale #2

http://www.tf2outpost.com/trade/21390950

http://prntscr.com/467nxi

Sold for an aussie knife (1.3) + Craftable Strange Bonk Boy (4 keys) ~ 23.75 keys + 4 = 27.75 Rounding up to 28 = 1.5*0.9 = 1.4

Sale #3

Sold for 1 bud, 10 keys, and 1.7 keys in sweets, ~1.6

http://puu.sh/auTGU/d8d827a9f8.png

http://www.tf2outpost.com/trade/21563076