I'd never tell another photographer how much they should or shouldn’t sell their prints for, as I feel that’s something they need to work out themselves, i.e. how they value their time, what materials they are using, etc.
I price my 12x9.5 inch fiber toned prints which are mounted/matted with 4-ply conservation board at €85. That's the amount I feel I need to get for the effort put into making the print.
I'm usually the only photographer at the fairs I have done, except one where a digital photographer was beside me. He had similar size prints selling for €20 or €30 which were also mounted but with a thinner standard economy board. He sold a few more than me but so what, if I lower my price to try and look competitive to him, then I'm wasting my time making the prints in the first place. I'm not saying his looked crap, they didn't, they were just different and while some people thought I was expensive, others appreciated my work having spoken with me about the whole process.
If you are happy selling prints for the novelty of it, then fine, sell them cheap but my point is to make it worth your effort.