On request (more or less) trying again with slightly different range. Andrew suggested 4-4.66 might be a bit better than 3.66-4 ref, simply to prevent a too huge drop in price. Proof is copypasted from previous suggestion, with a few additions.

Not many on the market but they seem to have taken a hit, possibly because of the Filamental.

Unsold in current range:

http://www.tf2outpost.com/trade/11081436 4.66, 6 hours

http://www.tf2outpost.com/trade/11064749 4.66, 1 day

http://www.tf2outpost.com/trade/11038244 4.66, 2 days

http://www.tf2outpost.com/trade/11013866 4.66, 2 days

http://www.tf2outpost.com/trade/10964936 4.66, 4 days

http://www.tf2outpost.com/trade/11089873 5, 1 day

There are a couple more unsold within the range (couldn't find any sold ones, if you can please comment), I felt it wasn't necessary to include them all to get the point across.

Sold in current range:

http://www.tf2outpost.com/trade/11013923 (with thanks to ConVict | blind polar bear)

Lower than current range:

http://www.reddit.com/r/tf2trade/comments/1enzpi/h_dirty_apparitions_aspect_w_455_ref_or_robohats/ 4.55 ref, appears to have sold; isn't in his backpack anymore.

http://www.tf2outpost.com/trade/11005838 4.33 ref, unsold for 3 days

http://www.tf2outpost.com/trade/11016307 4 ref, unsold

http://www.tf2outpost.com/trade/11084854 4 ref, unsold

http://www.tf2outpost.com/trade/10704718 4 ref, SOLD very quickly (with thanks to ConVict | blind polar bear)

http://www.tf2outpost.com/trade/11091653 3.77 ref, unsold SOLD

http://tf2tp.com/trade.php?trade=9463673 3.66, sold

Buyers:

http://www.tf2outpost.com/trade/10189745 2.66, none in backpack

http://www.tf2outpost.com/trade/9109477 3 ref, one in backpack but trade has been up for weeks

http://www.tf2outpost.com/trade/10544998 3.66, one in backpack in two weeks

http://www.tf2outpost.com/trade/10601791 3.66 ref, none for two weeks

Any critique is welcome. I realise this is not much proof, but it's quite hard to find when there are 2 pages on Outpost, none on bazaar.tf, one on reddit and one on tf2tp.com. The range might not be perfect but is more accurate in my opinion than the current one.