Caribe Tours
I see the prices came down on some airfares. At least when I am going from NY to STI in September. I found it as low as $299 direct flight both ways from JFK. There is a company called Caribe Tours and I believe they can get you to Cabarete or at least Sosua for around $200 pesos, roughly six US dollars. I am going to use them when I go there. I think you said you have never been to STI. It really isn't that confusing because the airport is small, but you will have to get a travel visa for $10 when you get there as soon as you go downstairs to where you go to get your passport stamped and pick up your luggage.