There are "popular" minibuses and cars which pick up passengers all along the North Coast route and stop virtually anywhere along that route.
In "downtown" Puerto Plata the stop along the South side (Beller street) going towards Playa Dorada, > Sousua, > Cabarete.
Going West, you just wink'em down at the little "bus stop" just out of the Playa Dorada main entry. Going East from Playa Dorada, you just do the same on the oposite side of the main highway.
I don't know what the current going rate is, but I'd reckon it will be arround 20 Pesos from Playa Dorad to Puerto Plata and maybe 30, 40 or 50 to Cabarete... less than a buck or two... US.
... J-D.