CaribeTour data:
Lv Barahona 6:15 AM, Arr SD 9:45 3hrs, 30 minutes, one very brief stop in.
The guaguas and larger buses of Sinchomiba leave SD from a station just over the Ozama River, and pick up people along the way
They have no toilets onboard, as does Caribe Express, and make a stop at Cruce de Ocoa for 30 minutes, where you can get food and drink.
Last time I took a smaller guagua because it was about to leave when I arrived.
LV. SD 4:45 ARR Barahona at 9:15 5 hrs 30 min. Time will vary with number of stops.
Caribe Express has a website :
http://caribetours.com.do/site/portada/
There are 4 buses each way 6:15, 9:15, 1:45 5:15 is the same departure time from both SD and Barahona. Fare is RD$260.
Be at the station 15 minutes before departure, they do leave on time.
The AC can make the bus a bit chilly, a jacket might be useful.
Catch the bus from Pedernales at La Plazuela, just past the Arco and the big white stature of Casandra Damiron. Sit on the left side and travel by day, as the highway runs along the coast and the scenery is beautiful .
The Caribetour station is a several blocks closer to the centro from the Plazuela.
Feliz viaje.