There are tons of places to shop, if you are willing to put in the time and effort.
Ochoa Motors in Santiago is one of the major (maybe the biggest) car/vehicle importers inthe DR.
Espaillat Motors in Moca is famous for good deals.
In Santo Domingo, where there is very tough competition (like Santiago) you can find deals.
A lot depends on what you want. Look in the classifieds in the Listin Diario.
HB