Unsure how to add a link without a massive ream of text but I noted there are 3kw brushless (low voltage 3 phase) motor and controller kits on Ali Express for circa £130 that might serve as a budget entry into electric propulsion, coupled to 2 parallel banks of 4 18v drill batteries in series would give a 72V battery of 10AH if using 8 5ah aftermarket jobs, even old laptop batteries use the same 18650 cells I've noted.