Price 9 months old.

Sellers at 2.66:

http://www.tf2outpost.com/trade/23697483

http://www.tf2outpost.com/trade/23787913

http://www.tf2outpost.com/trade/23793838

Not really any others on Outpost as there are many painted/low craft ones and many people asking for "backpack.tf prices".

In the classifieds, however, are:

3 x 2.66 (of which one was listed in the TF2Outpost links.)

3 x 2.77 (of which one was listed in the TF2Outpost links. He asks a scrap more on backpack.tf?)

4 x 2.88

Looooots of 3 ref suggestions.

A range would be best here, as they do seem to sell for 3 ref. It just needs a bit more time than sellers for 2.66 (2.66 isn't a quicksell though, needs time as well!).

So there are 11 sellers below 3 ref to be found at the moment. Considering there aren't many people selling normal ones (no painted/low craft) and many people always ask backpack.tf prices, it's enough proof for this suggestion.