Need DC power sys. for 400 lb vehicle

The total vehicle weight including chassis and payload, minus drive system and batteries is projected to be around 400 - 500 pounds. The vehicle will be driven mainly on dirt and grass, with moderate slopes and hills, At no more than fast walking speed or below 3 mph. The drive system should either be "in axel" propel 2 wheels or independent propel 2 wheels. Reverse option is a must. Maneuverability is important. Motor gearing for small (garden) tractor tires or similar. Wheel chair control type if possible.