Fastest: Private car/taxi
Cheapest: Guagua
Punta Cana/Bavaro -> Higuey (express bus, 1 hr)
Higuey -> Hato Mayor (express bus, 1 and 1/4 hr)
Hato Mayor -> Sabana de la Mar (local bus, 1 hr)
You may also want to check this thread
Uvero alto - sabana de la mar