Cab from POP airport to Playa Dorada is 250/300 pesos (about $25 Canadian).
Tour of POP, Amber mueseum, then off to spend the day at the beach in Sosua is wonderful! You can also shop at the large open air market along the beach and go snorkelling for a very cheap price - great fish!
The Playa Grande beach tour is great too - it's an all day tour that includes a trip to a family's plantain, lunch at a great local restaurant, and the afternoon at one of the most beautiful beaches - very large waves!