In Las Terrenas, we stumbled on a small place (sorry can't remember the name) in Playa Bonita, a bit out of town but very quite and peaceful. There are some small hotels there that offer B&B. The one we stayed was nothing special, but right infront of the beach and nicely decorated (no Air Con or TV). Shower and hot water, double room for $60USD (per night with a small breakfast) . It's the first hotel when you arrive from a very bendy and full of potholes road (Playa Bonita is sign posted as you come to town from Nagua side).
Although there is nothing around at night, some hotels offer drinks and food but very quite, for more night action stay at Las Terrenas town center/beach.
In Samana we stayed at the Chino hotel/restaurant up the hill (run by Chinese of course), you can't miss it just look up from main road. $3000 pesos for two double rooms for one night (no breakfast). One was very small and no windows (I wouldn't call it a single even), the other was nice and large with a balcony with a view of the bay, both with cable TV and Air Con, shower and hot water (make sure you haggle, they wanted $3500 first !?).
Not much to do/see in Samana town itself (day or night ! ) but a few things to do in the area (check posts here...).