Resuggesting.

Classified ads at the time of posting:

http://m.imgur.com/iQidHhx

http://backpack.tf/classifieds?item=Starduster&quality=6&tradable=1&craftable=1&australium=-1

1*3.8 keys

1*3.82 keys

1*3.92 keys

6*4 keys

Sales at 4 keys:

http://imgur.com/a/QsHqa (Credits to Linus)

Unsolds at 4 keys:

http://www.tf2outpost.com/trade/27902674 (~4 days)

http://www.tf2outpost.com/trade/27897945 (~5 days)

Unsold at 3 keys and 18 refined (~3.9 keys):

http://www.tf2outpost.com/trade/27627041 (~2 months)

Seller at 3 keys and 15 refined (~3.75 keys):

http://www.tf2outpost.com/trade/27895302 (~6 days old)

This is all I could find on Outpost that are valid at the time of posting this suggestion.