NASA’s Jet Propulsion Laboratory has designed a driving 6-wheel rover with almost the same suspension system as the real rovers on Mars, but using commonly available components that your students can buy online and assemble in a garage. They provide the the parts list and the build instructions, your students provide the hands, brains, and elbow grease to put it all together.
The downside is that the parts run about $2,500. The good news is that others have already come up with cheaper versions (see Swappy the Rover).
Check out the drive-the-rover-yourself demo on the main page!