I've done this a few times. Mostly for industrial design projects like product bezels and cases and such.
I usually "carve" something out of wood and paint to get an idea of physical appearances, fit, etc. From that I'll usually make a fiberglass model (so that I can test fit something that is close to the actual dimensions/thickness of the actual item). Then I Google for a local freelance CNC shop in my area and commission a formal CAD drawing and prototype milled out of a plastic.
From there you can generally figure if your design is right for injection molding, vacuum forming, etc. Find the right CAD guy and they can often help guide you somewhat with the design as well.
I usually "carve" something out of wood and paint to get an idea of physical appearances, fit, etc. From that I'll usually make a fiberglass model (so that I can test fit something that is close to the actual dimensions/thickness of the actual item). Then I Google for a local freelance CNC shop in my area and commission a formal CAD drawing and prototype milled out of a plastic.
From there you can generally figure if your design is right for injection molding, vacuum forming, etc. Find the right CAD guy and they can often help guide you somewhat with the design as well.
Happy to help if you need more info.