Alot depends on if you are selling in a commercial sense, for instance to a company for use in their advertising, or a portrait of a person or as fine art. Art should always be more expensive for several reasons. For an fine art print you are selling a print that is intended to be displayed for a long period of time and therefore needs to be printed in the most archival way possible. And I do not print alot of prints of the same image, just like a painter will not paint 100 of the same painting. An art print should be printed well, matted and kept away from the glass and framed or ready to be framed by the consumer. I charge for a 16x20, which is usually the smallest I will print for $450.00 and I go up from there. A fine art print that is hanging in a gallery is much more. Do not underprice yourself. The problem comes in if you try to raise your prices and you have gotten a word of mouth referral they will be rather upset when you have higher prices for them. Been there, done that. This is especially true for wedding photographers. The best thing to do is join a photographic association or group, for instance ASMP, PPA, WPI. Fine art is a different matter and you should check some near by galleries to see what some photographers are charging for their art prints. I don't sell negatives or my copyright and I will never sign a contract for work for hire. Always have a contract and invoice for all of your work, even for an art print. Again those photo associations and groups can help you with the wording of those contracts to cover yourself and your client. I hope that helps.