I put my printer up on a previous website like yours. That website based their price on weight and print time. The result was that I got a lot of orders for tiny items and never any orders for large runs. The setup and packing time time plus packing materials for a small order is just as long as for a large job so I was not making any money and it was just a huge pain dealing with these tiny fragile parts.

Can you please clarify how you are going to handle pricing? My preference would be to let suppliers bid.