o\ just started reading here. if you are just printing for other people to earn money, you will probs want to charge close to £2-£5 what you have got to include is, time setting up the printer for the next print, and also to cover any failed prints, the more printers you have and the more jobs you have will obviously make you more money (3 printers printing at the same time will always be better than 1)
Design then print for some one, this is a tricky spot as it depends on your experience with designing parts, you have also got to be aware that the first test print is always that, a test fit and will probs require modification to fit or its intended use, costs can run very high depending on what you are doing
designing your own stuff printing and selling it.
an ornament as much as you can make it look good and people will like it, is not worth any real money
a new tool or a replacement part for something, This is where if you find the right part can actually start to make you some money, you just then need to market your product
Designing toys or complicated things requiring lots of parts and printing them, This is something you can invest all your own time in, but with out doing some research of looking at what others are doing and doing it better etc, this again will need you to market your product.
designing stuff and sticking the files online, pretty much the same as the above designing toys / complicated parts, just less labour costs and dont need 1-how ever many printers