Labor to build a single wheel is about $40-50 at the shops around here. Plus another Sun CR-18 rim. Reuse spokes, nipples, hub, tape, tire. That's what I'd do, if he can't true the existing rim.
I would not buy a cheap pre-built wheel because then front and rear hubs and rims won't match (which would bug me, and hurt bike's value), and a hand built wheel will be better.