I recently purchased a ROVER 5 Robot chassis.
Considering that this is meant for 'Hobbyist's' and has a very reasonable £49.99 price tag in the UK. It is still an impressive chassis, with the useful feature of adjustable height to give optimal ground clearance. The one above has 2 motors and 2 quadrature encoders. Option include replacing tracks with 4 x wheels and a further 2 motors and encoders making it a 4WD. The chassis now also comes in Military Grey.
I am writing a review of the chassis, and have included easy to follow instructions to adjust height.