Beach Access

So I am considering staying at GBP La Romana. I know it's not the best place but the price is right and we like to get out and explore anyway. So the question is...are you able to access some of the better beach areas with a car rental? What else is there to do with a rental? (In the La Romana area only - have explored PC, Juanillo, and Bavaro areas.) We feel trapped having to stay in a resort for more than a few days so I'm thinking one of the better hotels (I would pick Iberostar) wouldn't be worth the money anyway. Opinions? Suggestions?

Also - are Isla Catalina or Sanoa at all worth a trip? I'm not interested in excursions, more of a do it yourself type deal where we can take an inexpensive ferry. It seems as though that may not be an option.