Buy ground beef, beans, rice, and tortillas in bulk (or even cheaper, make them yourself—it’s not hard!) and be smart about planning to use vegetables and other perishables efficiently across multiple dishes, and you’re going to be making Taco Bell menu items at home that are far superior to Taco Bell for much less than $5.
Buying hotdogs, buns, and soda in bulk will probably cost ~$1.25 per meal, if not less. You can freeze the dogs and buns; the latter will still taste great after a light toasting.