You said 'Where is the cheapest source of these "1000rpm" gearmotors everyone talks about?'. Others can advise you better than I but you can get free motors, or very cheap ones, by picking up a couple of old electric screwdrivers at a swap meet or garage sale. As with electric drills, these go for little or nothing once the batteries go bad. They are slower than ones made for robots but they are rugged. First robots are often a learning curve; if I were you I'd build something in time for the next event near you, fight it, and then build a new one based on what you learned and using the electronics from the first one.