Hi there,
as I understand You've never done anything robotics related, hence I suggest to start with
$50 robot. It is described in detail, plus it will give You great board for further development.
Or if a look-a-like is too difficult, then what would be a good start?
If You want it without any fancy features, than (as mentioned before) $50 dollar robot board and slightly modded chassis will do. Detail of a body of the robot will depend on how well You can use tools. To mimic appearance of Mars Rover...
...I would suggest using soft material - something like solidified foam (I'm not sure about exact name), it normally can be sliced using hot wire or any other hot tool for that matter, or can be easily cut using plain kitchen knife. It can also be painted with paint that does not contain any thinning liquids or acids.
