Right across the street from Taqueria Los Coyotes is another favorite cheap eats destination, Pancho Villa Taqueria. A fairly good taqueria in its own right, the true value of this place shines during it's happy hour from 3-5pm on Monday-Friday.
The tacos come with your choice of meet topped with onions, cilantro, and salsa. They have a dozen different meat choices, so there's something for everyone. I liked the carne asada and carnitas. During regular non-happy hour prices, the tacos are $3 which is a relatively steep price, especially for a small street-style tacos, but at only $1 they are a great deal and well worth the price!
Though many places advertise $1 tacos, such as The Taco Shop at Underdogs and many other "Taco Tuesday" type deals, Pancho Villa ups the ante by offering $2 beers and $1 agua frescas. The beer selection is limited, with choices being Corona, Negra Modelo, Tecate, and a couple others, but at only $2 it's hard to complain about them not having your favorite microbrew on tap. The agua fresca selection may be the best I've personally seen from any taqueria in San Francisco. They have many different flavors, including horchata, pineapple, papaya, strawberry, watermelon, cantaloupe, lemon lime, and others.
To top off an already good deal, you even get a little basket of tortilla chips with your order and they have a variety of salsas and condiments at their salsa bar, which according to all the medals decorating the wall, are award-winning. I found them to be pretty good, but nothing to write home about.
For two tacos and Negra Modelo, I spent barely over $4 and was completely satisfied. It was like I paid for a beer and got free tacos and chips! Pancho Villa Taqueria is located right off the 16th & Mission St. BART station, and is open daily from 10am to midnight.
For more info: http://panchovillasf.com/