Personally, I always try to build things myself if I can. If you have the tools available, try designing and building a custom robot...that way your robot will be original and different. You can get most of the building materials needed for such a project at your local hardware store. Some materials to work with would be L-shaped aluminum/steel bars, aluminum or steel sheet metal, acrylic/polycarbonate sheeting, HDPE (high density polyethylene), wood etc. If you don't own the tools, see if your local hardware store can provide a workshop for you. I know the Rona near me can rent out their workshop for $15/hr.