Proof below. 10 month-old price.

Sales:

http://www.tf2outpost.com/trade/16591378

-wanted 5 buds

-sold for scorching salty=5 buds due to b/o

http://www.tf2outpost.com/trade/18716300

-b/o of 5 buds

-sold for stormy 13th whoopee (slightly outdated)+pro frontier kit=close to 5 buds

http://www.tf2outpost.com/trade/18403237

-looks to have bought koga's ghosts belt (before update)+vivid handle (outdated): http://www.tf2outpost.com/trade/18440368

-~4.3 buds

http://www.tf2outpost.com/trade/18124986

-wanted 5 buds

-panama+few keys bought ghosts panama+steaming stash: http://www.tf2outpost.com/trade/17885609

-~4 buds

Current trades:

http://www.tf2outpost.com/trade/18014232

-looking for ~5.5 buds, 1-2 months

-notable offers:

secret mirror=3.7

pe fez (using price now)+o.f. fruit=4.5

ra hermes (outdated)=4

scorching robin+6 keys=3.9

5 buds collecting

http://www.tf2outpost.com/trade/18970641

-wants 5.2 buds

-notable offers:

blizz impaler (slightly outdated)=4.7

Sales: 4, 4.3, 5, 5

Range of 4-5 based on sales and offers that fall within this range. Buyers don't seem to be willing to go higher than 5.