I've been getting into playing with Arduino's and Photons, and have some ideas that I'd like to THINK about taking to market, but all of these sort of intros seem to stop at the PCB stage. They leave off the part about how to get an enclosure made - designing one, prototyping it, injection molding, etc. I think it's because that's where things get really expensive...
Also, designing a enclosure is a completely different beast. Nowadays you would typically start out by 3D printing stuff and then later on in the process get it manufactured by injection molding. That means going to the factory and making sure that everything is set up right before they start the manufacturing the part. Again a very ad hoc procedure that's unique for every product.