We just had lunch at the 2nd Street Cafe on 7th Avenue in Park Slope. We haven't tried their full entrees yet, but they have great sandwiches for $6-7. They're on nice breads and are served with either fries (not as good as Bonnie's, but good) or a mesclun salad. They also have fixed price lunch and dinner menus. I'm new to this message board, so maybe someone's covered this already.
Also, there's that fabulous fixed price lunch at Soto Voce!