If looking for a non-expensive tapas bar with local food and atmosphere, I would say Bar Malasang, located at Eixample meets all these requirements.
I love the space; it has huge windows so there is a lot of natural light. The casual interior design with big wooden tables and refurbished furniture make you feel very comfortable and warm. It is a bar where I go often because I feel very cosy when having a beer or a glass of wine there with friends.
At Bar Malasang you will have typical authentic Catalan dishes made with fresh ingredients. Simple but really good quality. I always have different plates to share. I usually start with at least the “patates tarambana” (their kind of “patatas bravas”) and the calamarcets (squid). If you are there for lunch or dinner, you cannot miss one of their toasts like the burger with eggplant, brie and mustard; or the chicken, caramelized onion, cheese and plum. No matter which one you pick, all of them are just delicious!
If you are a cocktail fan, I recommend giving their Moscow Mule a try!