Unless you get lucky and find a used one near you you're better off just buying a new one. You see if you find a used one you have to pay shipping which would be outrageous on a beach cart so in the end you're better off buying new from TBM or Bigfoot where they will ship it for free.
You can get a new TBM or Bigfoot for $450-500 shipped. You figure if you find one used for 250-325 and ad 75-100 for shipping you're already up near the price of a new one and with a new one you don't have to wait to find one.
My .02