Someone asked the same question here a while ago, and I suggested to him the Aparthotel Lomar on the Malecon. I've stayed there repeatedly in the past, and I like it a lot. Clean, with security, spacious rooms, balconies, security, TV and not least, reasonable rates. I'm not up to date on the rates, though, but a couple of years ago they ran at like RD$ 500 per room and night. There's a snack bar on the premises, and a restaurant next door.
I don't have the phone number, but you should be able to find it by way of Google or whatever.