Pricing only has a little to do with the material costs and if you're selling prints then these wouldn't normally be the first final print off the negative. If you're having to make a dozen or more test prints then there's something wrong with your negatives, and you should be getting a higher success rate than 1 good image every 4-7 rolls of film.

Price is about what you feel the market will stand for your images, you might also take onto account what others (similar to yourself) are selling images for.

It's rare that it takes me more than 3 sheets of paper to achieve an exhibition print, but I can read negatives which comes from experience so I know where to dodge & burn before I start and I can usually judge the contrast needed as well.

The secret is getting good negatives by good control over exposure and development, it's not difficult but a little effort to nail your personal EI's and Dev timses for one film under various conditions means you can concentrate on the photography knowing once capture you can get excellent prints.

Ian