hey,
i'd look into a 2nd hand but reasonably new PW50 something like this:
YAMAHA PW50 2004 - eBay Yamaha, Trail Bikes, Motorcycles, Cars, Bikes, Boats. (end time 24-Jan-09 10:14:33 AEDST)
Don't bother with 50cc chinese bikes, as he may have to spend more time getting it fixed then riding it...