I would like to get 2000 parts of a small 2.5" x 2.5" product made to test market it. It's not economical to have it 3D printed in this volume and it's not economical to make a cheap aluminium mold for a small production run. Here's a guy who made a 3D printed plastic injection mold and made parts with a desktop injection mold press. http://www.rhinofablab.com/profiles/blogs/rhinomade-3d-print ed-mold-for If I made the 3D printed mold, is there anyone who would like to make 2000 parts for me using this process? Or does anyone have a better idea?
Proto Labs has a service called Protomold that is well matched to your application. Aluminum is probably your best bet, and it is fairly affordable. If a few dollars per part doesn't work for you, I have to wonder whether what you are selling is worth making. Plastic things with a value below that quickly end up in the trash, and producing such objects does not make the world a better place.