$600 is a bit pricey on either ... but the garelli (in my opinion) might be worth that much. if it's in near-mint condition and runs great, then i might drop that much for a classy moped.
if the honda needs work at all, it's not worth more than US$300 (or a bit more).
i think $300 is fairly reasonable for a running moped w/o any problems. maybe a bit more for a really rare or "dream" moped.