Sukie,
Rather than pay more than 2000 pesos for a taxi to Puerto Plata, you could take one for 200 pesos or so to the Caribe Tours terminal. It is near the main rotunda for buses in Santiago. If Caribe Tours doesn't have a bus going to Puerto Plata, there may be a mini-bus going there. The Espinal bus terminal is also there. It probably has more buses than Caribe Tours anyway.
If all the buses have quit running, then worst case you can stay at Hotel Rotunda for probably 500 pesos. It's pretty good for the price. There's several small restaurants next door. There's also a MacDonald's 2 blocks or so away. There's even a Car Wash a few blocks beyond that.
Since you'll be on vacation anyway, that might even be a nice little diversion - better than arriving at Puerto Plata too late at night to do anything.
If you don't like that option, send me a PM and I can put you in contact with an English speaking taxi driver who would drive you to POP for probably only about 1000 pesos - or will even show you around Santiago.