If you're looking for inexpensive, typical foods prepared Catalunyan style, I highly suggest trying RESTAURANTE POLLO RICO at #31 Carrer de Sant Pau in the El Raval section, two blocks off of La Rambla and down from the Gran Theatre de Liceu. Actually, there's two restaurants within the same location. A fancier one upstairs...though I never made it in lieu of bellying up to the downstairs stainless steel counter top shoulder-to-shoulder with all the locals and being welcomed into their everyday lives. The place runs like an old diner with foods prepared across the counter. Service was quick/efficient, the food large proportioned, good and inexpensive. The place was always packed, but it's worth the wait for a barstool to open up.
As you might suspect from the name, the house specialty is rotisserie chicken, but check out the menus which come in several languages. Beef and pork dishes are also excellent as well as their higadillos de pollo - chicken livers pan sauteed in wine and garlic. Everything is served a la carte, but the prices are still VERY inexpensive. A typical meal of appetizer, salad, bread, entree with potatoes, side dish, bottle of wine and after dinner drinks ran $12-$15 at most! Of my 10 nights in Barcelona, I dined half of them here. It's a definite must for local flavor - both the food and the people!
BAR RESTAURANTE ROMESCO is also nearby and addressed as #28 Carrer de Sant Pau, but is actually entered from a side street called Carrer de l'Arc de Sant Agusti. The place isn't well marked, but the cooler with all the fresh foods fill the front window. It doesn't have Rico's atmosphere; you can dine sitting at the counter or at tables. However, the food is just as good, large proportioned and priced the same. One of Romesco's specialties are "frijoles" -cuban-styled black beans served with rice, a chili-like meat sauce, fried sweet platanos, and topped with a fried egg for 550 pesetas...you won't need or want much else! They also serve the famous regional sausages from the town of Vic prepared several different ways. Here was a nice, convenient break from Pollo Rico, but if you've to choose between the two, Pollo wins belly up!