Ahhh yes, Mexican food! San Diego certainly has its share of many fine Mexican restaurants and eateries. No doubt, I will leave out many, unintentionally of course, but three simple, good and inexpensive ones that come to mind are:
Roberto's (Del Mar)
Situated on Carmel Valley Road alongside Los Pe~nasquitos Marsh, this unassuming outdoor restaurant serves an excellent carne asada burrito. The combo plates are pretty good too! A great stop on the way or from the beach. Make sure to bring sunsreen!
http://www.robertos.us/main/index.phpLas Cuatro Milpas (Barrio Logan)
Centrally located in one of the oldest hispanic quarters of the city, this home-style restaurant has been a fine San Diego establishment for decades. The food is simple, delicious and a great value. My favorites are the chorizo and tamales. Make sure to arrive early as the line starts to form before noon.
http://entertainment.signonsandiego.com/places/las-cuatro-milpas/Clayton's Take Out (Coronado)
Who would think that a place called Clayton's would serve a gigantic delicious burrito for a few bucks?? Well, if you're in the neighborhood and would like to carry out good Mexican food to the beach or a park, this is worth a stop. Parking is rarely a problem on any of the nearby streets and food is ready to go in minutes.
http://maps.google.com/maps/place?sourceid=navclient&rlz=1T4SKPB_enUS309US309&um=1&ie=UTF-8&q=coronado+mexican+restaurant&fb=1&gl=us&hq=mexican+restaurant&hnear=coronado&cid=4637047693533663521Three notable sit-down mentions are The Old Town Mexican Cafe (Old Town), Fidel's (Solana Beach) and Karina's (Chula Vista).
Happy Eating!