There are three choices out of San Juan: Carnival Victory, Celebrity Summit. and Royal Caribbean Brilliance. Carnival is the cheapest but I think I would rather do one of the others. My budget and backpacker mentality guides me to the cheapest room. I've seen some great prices at the agency that works with Delta employees ... my son is a Delta pilot. Should get a new price list tomorrow, the 21st. Will propose dates then.
I will go down to PR
early to check out the places where I worked and lived in '75-'76. I'll rent a car. There is a hostel in old San Juan but two could stay as cheaply near the Condado beach and airport.
I planned to rent a bike on each island. Not necessarily cheap, but far less costly than ship tours ... and no customs worry.
If you want to talk about it let me know and I'll send my phone number in a private message.