4 days in Barcelona, looking for reasonably priced, delicious, local places for meals...
Below are links to earlier posts on eating in Barcelona during August:
As to what places are actually open on the days you are there, you'll have to do the leg work and contact the places that interest you.
I was in Barcelona last winter and we ate at Mussol on several occasions. I think they have 3-4 different locations in Barcelona. They serve traditional catalan food. It is very good and is definitely reasonably priced. We didn't see any Americans/tourists there the entire time.