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Then add a cheap battery and charger and you're pretty much set for around 500 bucks, which is in the price range of a new HD2000, AND you get to feel like a kit on Christmas assembling your new LEGO kit
This would require basic circuit knowledge to follow pin outs on the boards for motor, sensor and battery connections, as well as soldering experience for both the board and motor leads, then heat shrink your wiring harness and make it look all pretty.