When it comes to cheap grub, nothing beats the San Francisco tradition of the hofbrau. Whether the food is palatable or not is debatable.
However they can be insanely crowded and a little red-eyed and sloppy.
A wholesome, friendly alternative is the Chick-N-Coop. There are actually two of them, but the one in the Excelsior is definitely the best. Owned by a Greek family who likes to banter with customers, you can’t get more of an old school neighbourhood vibe than lunchtime in one of its olive leather booths. And true to its name, the chicken is a pretty tasty bird.