Hi. I work for a company that does a huge amount of prototypes for all types of companies and industries. I would recommend using Google's sketchup over all the other options. It's free and gives you much better results than other software packages, even the ones you pay for. Doing something in rhino looks nice on the computer but is a huge pain when you go to actually create it because it doesn't have basic mechanical structure to it.

Check out www.protocafe.com They do a great job with everything i send them. Cheap and professional.