That all depends on your popularity and the quality of the work, if your name is known then you can charge more, etc, depends on how it's framed and matted as well, custom framing is costly so sometimes they want to customize but other times they want it already framed. This whole things is highly subjective.
I am not popular at all but I try to use the best frame and glass.
It is even difficult to find more photographers printing that small to compair.
Well it's been a while since I first posted the question and I have now come to the conclusion that I will not do limited editions. I'm way to messy for keeping track on which number I'm on, since I don't want to print a whole series in one go. And why should I limit myself? It will happen naturally since I quickly get bored with an image. I now feel more confident dealing with galleries as well. It's easy to get hung up on things when you are insecure and when people "in the business" tell you how they want you to do things. In the end it seems to work out better when I do what feels best.
A lot of interesting thoughts in this thread though and I do like the idea of numbering prints!