Direct drive motors, while heavy, only have one moving part (except bearings/bushings) and have been reported to provide thousands of miles of good performance. Look at xcerries on ebay (put 36V 500w into your browser). The kit should be about $200 delivered. Add $600 for a 36V, 20 a/h battery (Luna Cycle) and you should squeeze out 30 miles at 20 mph. Not necessarily a better solution, just another consideration.