The cheapest is a ferry that runs from Santo Domingo - Mayaguez, Puerto Rico, then take a bus to San Juan. However, it costs $60 US each way, And if you want a cabin, it is $60 US more. Plus, you need to eat one meal aboard, which is not cheap, either. Then, take a bus from Mayaguez to San Juan (about $10 US/person). You are on the ferry from 4:00 PM until 11:00 AM, and if you don't have a cabin, you have to sleep on the floor or on tables in the cafeteria. NOT alot of fun. They do have a lounge, serving drinks at about $4 US/drink, and that will occupy you until 2 in the morning (live band aboard), but what do you do for the next 9 hours??? We probably would've saved money by flying. AND DO NOT, if you are Canadian or American, let them tell you that you need to buy a round-trip ticket. You only need to buy a one-way - it is not cheaper to buy a round-trip ticket.
Much easier and faster is an American Airlines flight, which will run you about $189 US return (I think?!?!?), and is much more comfortable and of course, faster. Personally, I would never take the ferry again.
PS
While you're in Puerto Rico, they have ferries going to the US Virgin Islands for about $60 US return. Also, in Puerto Rico, stay in Old San Juan. I loved it. Was only going to stay in Puerto Rico for a week or two, and ended up staying a month. If you are going in February, make sure you hit the San Sebastian Street Fest! E-mail me if you need more info on Puerto Rico or the DR.
