A lot, a whole lot depends on where you are
In the northern part of the country, nobody can compare with prices from Ochoa. I do believe that Dep?sito Ferretero in POP has a good service for concrete, however.
The cement companies do not sell in small lots so you have to go through a building supply company and Ochoa operates both in Santo Domingo and Santiago.
In fact, just so you know how the game is played here, Ochoa has supplied an awful lot of the building supplies for the hotels out in the east!! Even cinderblocks and re-bar. How can they do that you ask? Well, the former owner of the place (R.I.P.) once told me that part of the secret was that his trucks delivered to the east and when they came to Santo Domingo they picked up stuff for delivery to Santiago and he saved thousands on transport. The guy was a balls up genius at making a buck...He'd send a truck load of cinderblocks to Santo Domingo, off load them, pick up a load of re-bar at Metaldom, haul it to the east, come back to Santo Domingo, pick up another load of re-bar for Santiago! Or variations of this.
Give us a bit more info and we can point you in a good direction.
HB