if you like to stay in a resort with a beach you can swim in just stay in one of the resorts in barreto. with your budget i would suggest playa papagayo, mirage or arizona..
if you want to stay inside the former base, you can stay in one of those resort/hotels near the board walk. lighthouse and marina are good places but are pricey. subic park hotel or bayfront hotel are more affordable. it will be nice to stay in these places if you plan to go on a gimmick in the evening.
enjoy your trip!

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