Resuggesting according to blind polar bear's comments.

Last accepted suggestion was based off offers. This one is based off sales.

The price shown differs greatly from the original suggested value.

Sold for a vivid plasma soldier's stash (4.2) + orb. fire beak (2.5): 6.7 buds (since the seller's b/o was at 6 buds, considering this an outlier):

http://www.tf2outpost.com/trade/16138346

Sold together with scorching mirror for burning noble (9.4, the 2 unusuals were offered): 5.9 buds

http://www.tf2outpost.com/trade/15946327

Sold with 10 keys (0.53) for purple energy towering (7, suggestion pending) ~ 6.47 buds:

http://www.tf2outpost.com/trade/16497048

Sold for 6 buds pure:

http://www.tf2outpost.com/trade/15557871

http://backpack.tf/id/76561198080141400?time=1388390400 - after

http://backpack.tf/id/76561198080141400?time=1388217600 - before

Blind Polar Bear's part:

http://www.tf2outpost.com/trade/16339381 - b/o 5.6 - short history too

http://www.tf2outpost.com/trade/16272273 - b/o 6

http://www.tf2outpost.com/trade/16830410 - b/o 6

http://www.tf2outpost.com/trade/16935474 - 5.7

With so many available for less, looks like this should be ~5.6-6.