Las Brisas on the corner of 10th and 4th is a great place for seafood.  Average about 7.00 usd for fish of the day with vegetables,etc.

Also, the best place for beef in Playa is Super Carnes HC de Monterrey on Avenida Constituyentes near 30th Avenue (open from noon to midnight).  They are a hole in the wall restaurant but for $100 pesos you can have "arrachera nacional" (steak), baked potato, 1/2 avocado, hot sauce, tortillas and a soft drink.

El Fogon has some of the lowest prices in town for authentic Mexican grill foods (no chicken or seafood, but all other meats).  Three locations: 30th Avenue & 32nd Street; Avenida Constituyentes near 30th Avenue; and 30th Avenue between Calle 6 and 8.  Tacos el pastor cost 5 pesos.  Everything else is very inexpensive.

The taco carts down by the bus station (5th Avenue & Juarez) are all tasty and very inexpensive.