Planning vacation to Puerto Rico...advice!! help!?

we're planning a low budget vacation to puerto rico...i found a hotel in fajardo that is really reasonable (found it on expedia). the thing is, i can only find flights from BWI into the san juan airport, and the hotel in fajardo is 1.5 hours from the san juan airport which would be extremely expensive if we took a taxi. i though fajardo would be nice because i read about a nearby rainforest and a beach nearby too. also we thought we could take the ferry to culebra or vieques and see those islands (like a day trip, not staying there overnight) but now im not so sure what to do because the san juan airport is so far away i do not want to pay out the nose for a taxi to/from airport to hotel. and i don't think renting a car would work because my mom isnt too good with directions and neither of us travel very often. what do you recommend? and is there somewhere else economical (like $600 max/per person) that we could stay in puerto rico that has various things to do (like beach, rainforest, other islands)