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 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.com
You can find cheap drafters on craigslist who can make a solid model of your part that you would ship to the machine shop.
I second http://www.emachineshop.com
The software is fairly easy to use. You can get your prototype built in pretty much any material you can imagine, and the price is pretty good too.
My only problem was the cost to ship custom cut boat glass to Alaska. Ouch.
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.com
You 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