If you cannot locate someone to share, also consider taking the inter-city buses. It would be one from Punta Cana to Santo Domingo -- less than three hours. And then we would suggest overnighting to see the Colonial City or staying two nights.
The bus service to Puerto Plata is good. You have a choice of Metro or Caribe Tours. Both are reliable, they leave on time, and have many departure times. You could take the Metro that arrives to Puerto Plata and then overnight in Puerto Plata city to see the attractions there, prior to heading to Cabarete.
Of course, you could make an intermediate stop in La Romana, prior to taking the bus to Santo Domingo.
Here is our La Romana guide.