+1 on Pappasitos and their sister resturant, Papadeaux http://www.pappadeaux.com/location/?id=125 (Pappasito's is texmex, Papadeaux is more creole/cajun with a seafood focus). Both are in A and have a really awesome atmosphere. Neither are probably considered "cheap" eats though ($15 pp min probably, after tip, tax).

In D I like Cantina Laredo. It's pretty decent typical Texas texmex. Probably can get by at $10 pp.