There's this little dive, hole-in-the-wall taqueria type place next to my school which I recently discovered on Yelp called Los Comales. It's off a busy road and if you're not paying attention, you can easily miss it.
I ordered 3 bean & lettuce tacos for $1.50 each and a guava agua fresca for $2. I asked the nice lady not to put rice in the tacos and just serve them on the side.
Damn, I wish this place was closer to home. They had a big 'fixins' bar so I added the rest on myself. I started off with radishes, salsa verde, pico de gallo & cilantro. Holy crap, it was so good! Total came to about $6. I will be going back often.
*EDIT- I've gone a gazillion times since but changed my order to 2 tacos instead of 3 because I would get so sleepy in class! Also tried the bean & cheese pupusas- also delicious with the fixins'.