I checked, JIC, and the
last bus to Puerto Plata from Santo Domingo leaves at 7 p.m., so you should have plenty of time.
The taxi fares from the airport to Santo Domingo are posted on the wall and on billboards as you leave the customs area of the airport there in Santo Domingo. Please tell the driver what you are going to pay-as per the posted rate- before you get in the taxi. It might even be a good idea to see if there is anyone on the plane that will be taking a taxi to Santo Domingo so you can share.
There are taxis that meet the bus as it arrives from Santo Domingo, so you won't have any problem getting to your hotel. Again, negotiate the fare before gettin in the cab.
Have a nice trip
HB