Cool project! Very cool that you'll be able to sell them.
It seems like whenever I talk about 3D printing at work (that's all the time), someone always suggests that I use printed parts to make my own metal castings. It seems easiest to do something like
lost-ABS investment casting, taking advantage of ABS's low melting point.
Seems like this would be the perfect project to try this out. Where you have mating surfaces, you could add additional thickness and clean them up in a mill to get closer to the requisite surface finish.