There are lots of restaurants in the Las Canitas area of Buenos Aires. I ate at three and this one was my favorite.
It's located right on a corner with interesting well-dressed people walking by. You can sit inside or outside. The food and service were excellent.
For 25 pesos (US$9), my friend and I had a delicious dinner with bottled water, freshly squeezed orange juice, steak with mashed potatoes, and ravioli with mushroom sauce. The menu also had pizza, other types of meat, pastas . . . very varied. You'll definitely find something you like.