Proof below.

3 month-old price.

Sales:

http://www.tf2outpost.com/trade/14539501

-looking for 5 buds

-sold for c9 marauder+1 bud=~4.5 buds

-offer of c9 bunsen=3.9 buds

http://www.tf2outpost.com/trade/14282996

-looking for 4 buds

-sold for sunbeams gonzilla+spats+g. dashin+vintage tower=~3.6 buds

Current trades:

http://www.tf2outpost.com/trade/14669954

-looking for 5 buds, 2 days old

-no notable offers

http://www.tf2outpost.com/trade/14639642 (relist, closed)

-no notable offers

http://www.tf2outpost.com/trade/13022078

-wants 5.5 buds firm, no unusuals, 2 months old

-offer of 5 buds pure

-offer of cauldron pyromancer+2 buds+4 keys=~4.9 buds

-offer of ge cosa=4.5 buds

-offer of terror watt cosa=3.4 buds

Sales: 3.6, 4.5

Please take note that I have only listed notable offers around the range.

5.5 should not be in the range, with one trade selling for that for 2 months and no close offers. Low end is from the sale of 3.6 while high end is from the 5 bud offer which he should have offered on the other trade since they were looking for 5 buds. Most offers are within the range.