There are great buses with AC who goes from S.D. to Boca Chica, Juan Dolio, B?varo, Bayahibe and lots of other tourist destinations on a very regular basis. If you are just going to Boca Chica, I recommend you to take one of these buses from Las Americas. They depart all the time, so you won't have to wait many minutes for one to leave. They will take you to the parquecito in Boca, which is very close to the beach. Last time I went, the best place to catch them were at the place they loaded most of the passengers. If my memory serves me well, it was almost at the intersection of la Venezuela y las Americas. In my opinion they are very comfortable and I went with them daily to the beach. If you are willing to wait a week or so, I can check out the details for you since I will be going to Boca Chica anyway and I will be going by bus. Which part of S.D. do you live in? There are lots of good connections with las OMSAS to las Americas from all parts of town, so it's not too much of a hassle to get there. But like every public transport in S.D. (except the Metro), one has to have certain knowledge of the area to get where one want. It's not like Europe or North America where you have time tables, specified bus stops and maps with all the routes. Perhaps you already know this, in that case I'm sorry for taking up your time. Anyway, you may PM whenever you want. And I will try to remember to write again as soon as I have checked the details for you.