Best way to get good quality cheap motors is probably to use the motors and gearboxes out of an electric drill.

No dismantling your parents drills though

U can pick them up pretty cheap from Woolworths, Argos, DIY stores etc.

Other than that as Alan says Technobots is a great place for everything you need. Or this forum.

Have you considered getting sponsorship from any local companies or forming a Team with some other people to spread the cost?

Richard
Team Mayhem