Try Da Nancy. Not much to look at...and nooooo..not the cheapest place in town....but not terribly pricey (dinner for 4 with wine appetizers and four plates of the special seafood with rice...lagostino, camerones, calamari etc) ran us 2000 pesos (two years ago...before the peso mess up).
Still...not a bad deal...it is not on duarte so you wont be bothered with street people. Stick with the specials...as the regular menu is pretty ordinary.