Having recently travelled to Spain and visiting Barcelona, here are my remarks on local beer prices.
In the tapas and restaurants of the main tourist attention street, La Rambla (Barcelona) the beer prices are high – 0,5 l cost almost 5 euros and 1 liter is a little below 10 euros.
Smaller beers cost 2,5 – 4 euros.
Btw. large 1 liter beers should be considered an exception in Spanish pubs (they call their pubs tapas). Very tiny beer bottles (0,25 l) are much more common. So, better order two at once!

Popular beer brands are San Miguel, Estrella and Amstel.