You didn't say for what part of the island so I will just tell you the place I know in Santo Domingo.
If you go to the La Cadena at the end of Sarasota that is just north of the Anacaona II apartments and turn south at the T junction there is a place about a hundred meters down the road that rents cars, including a limo. Don't know the rates, I just passed it on the way to Cadena to do my shopping when I lived there. I just moved this year so it is probably still there.
