If he wants a stated load limit above 332 he may find it in a utility bicycle, post on that board. All you can do is give advice: steel frame, as many spokes as possible, small diameter wheel would make the bike stronger. Steel frame BMX with mag wheels?

I think cheapy walmart bikes might have indestructible steel frames, it is the wheels and pedals that will fail.

My guess is he can fish a suitable steel frame out of the garbage on recycling day. Most of his cash should be spent on that rear wheel.