Check out the prices at MAU on 27 de Febrero in Santo Domingo or on Bartolom? Col?n in Santiago. They stock Hankook tires which were the best I ever had on my '87 Jimmy Sierra Classic. They were great...and the prices were fair.
PriceSmart is also a good option.
Finally De Leon Gomas on Bartolom? Col?n in Santiago is a final option.
Cordially,
HB