Old price, needs update.

http://www.tf2outpost.com/trade/4318794 only one on OP

Some really good offers including 5 buds, 5 buds and 10 keys and several higher mixed offers but those are not very recent.

Also more recently:

Planets slug + buds + bills (~4.4)

5 buds

Stormy Brainiac (~4.2)

165$ (~4.7)

5 buds pure + blizzardy noble (~7.3)

So 4.2-5 seems fair as the 7.3 offer was retracted fast. Couldnt find others but i am quite sure ive seen one sold for 4.5-5 pure.