I took this ferry in January, and it's not all great. You pay $120 US, one way, and an extra $60 US if you want a cabin. Trust me, you are going to want a cabin, because it is at least a 12 hour journey, which travels at 8:00 PM. If you don't have a ticket, it is best you get there at 4:00, when the office opens. Then, they make you go through immigration, and you are stuck on the boat until 8, when you leave. The drinks and meals are very expensive, and if you don't get a cabin, the only place to sleep is on the floor of reception. When you finally arrive in Mayaguez, PR (about 2 hours from San Juan), you have another 2-3 hour wait for immigration. Basically, we were stuck on this boat from 4:30 PM to 11:00 AM! We decided never to put ourselves through this again, and called American Airlines. One way, to Puerto Plata from San Juan, was $171 US, and took 45 minutes!