We went to DePalm Island a few years ago and if my recolection is correct, we did not think it was worth the cost. It had a self guided snorkel as well and we did not see that many fish during our time there..They do offer lots of water sports and have a restaurant and facilities available to customers.
We went to Palm Beach on our own the last time we were in Aruba. The cab fare was around $20 each way. The beach had necessary ammenities, but the snorkeling wasn't very good. Still it was a nice way to spend the day.