JohnRender, The answer to your question is, "it depends." Some charge by the hour, other by what the market will bear. Some sell on e-Bay, others in a gallery. Some web-sites pay for groups of images, others single images. I know that's probably not too helpful but there's a lot to consider. Essentially, you need to pick your "business model" and use the prevalent marketing strategy ... and that will tell you how to price your artwork (provided it's marketable).