I would suggests contacting Mr. Shawn Herrera Luquillo Taxi. I got his name from Trip Advisor and we just used him for some short trips and back to airport from St. Regis Bahia Beach. I am not certain about just local SJU trips but I believe he could help you with getting to the ferry and I just had a conversation with him about actually getting tickets for his clients early morning. That ferry situation can be chaos and frustrating. Check with him 787-513-7685. Again he has some other reviews on TripAdvisor as well and is an excellent driver with very nice car and RELIABLE which not all drivers are. Just Google: "LuquilloTaxi"
more