Based on the simple criteria that 90% of the entrees on the Menu cost $10.00 or less, the food writers of the San Francisco Chronicle offered this month the 10th Edition of their Bargain Bites.
You can search Restaurants by Location, Category or Cuisine.
The Cuisine section offers the most diverse choice.
Beyond the obvious Chinese, French, Carribean and Mexican less traveled options are Burmese and Lao.                                             
I checked the lonely Moroccan option Tajine (no alcolhol, cash only)a small (7 tables) place.
The Kebabs cost only around $7.00. As for my favorite Couscous, you can fill up for $8.00 to $10.00.
Check their Menu which includes Vegetarian Dishes and Sandwiches and my substitute for a Hot Dog, Merguez.

So if you want a tasty, unexpensive lunch while exploring the San Francisco area, you now have a few options.