Keep in mind most if not all of those 3d printers require a watertight model to work off of. They can make it watertight for you if required but usually charge extra for that. They also will probably require the submitted model in whichever format their machine works with the easiest. I know alot of them use Inventor Pro which is an Autodesk product.
A Miniature enthusiast wanted some 3d starship models I created made into physical models. He has a friend with a 3d printer and is currently working on some prototypes. Of course we're talking really small models, around 2-3 inches. His printer does a max size of 8-12 inches and prints a master in a soft resin/wax substance. The master is then treated to be able to withstand vulcanizing. In some cases the master is sent off to be produced in a more durable material for the production of a mold. Unfortunately, at least with this dude, it's costly and a 2-3 inch master could run up to $75. I'll get copies of my models as payment for their use tho, so that's cool.