Mmm. Since I don't use Traditional Media I'm not entirely sure, but I do know that Pencil Sketches usually don't sell for much (~500g), but Copic Markers/Watercolor pieces of reasonable quality can sell quite nicely for a good sum of money. Obviously this depends significantly on the artist as well - if people like your art, then they'll be willing to pay more, and the same applies in the opposite situation.
I am currently running a commission shop (Which was established two days ago...=D) and selling for around 3k a CG chibi. All slots are full right now, so I suppose it's doing pretty well.
Hope this helps.