I would agree that those high-priced cab rides have to be from the far south AIs. I have stayed at the Fiesta several times and the Presidente once (they are less than a mile apart) and the cab rides have always been cheap. They also have posted prices at the hotels that the cabbies have to observe. Coming back from town, the same rule doesn't apply, but just remember what you paid to get into town and insist on paying the same, or maybe just a few pesos more, to get back to the hotel.
Christi is absolutely right about the beaches. Anybody from the Fiesta north that has a beach built it. I have always liked the Fiesta pretty well and it is probably the second-nicest hotel on the island, after the Presidente. Which, come to think of it, probably makes it the nicest for the time being. Staying at the Fiesta puts you that much closer to the main dive sites and the harbor is close, right next to the Presidente, in fact, so any of the dive ops will pick you up at the Fiesta's pier. If you are interested, I can give you some more information.