How does one prototype a physical product?
npk: How complicated is it?  Can you make it yourself?  It's probably best if you do.  If you have something you want to make in quantitiy, you'll want to hire someone who is experienced with tooling up a factory efficiently.  What you're doing is not really engineering, but more like "drafting".If you live in the bay area:
http://techshop.ws/If it's relatively simple, you can find a CAM house that will build the part for you, but then it becomes expensive.  This place has an FDM house (wikipedia for details):
http://www.emachineshop.comYou can find cheap drafters on craigslist who can make a solid model of your part that you would ship to the machine shop.good luck