As it happens, I just posted a blog entry on my first visit to Barcelona, which might give you a few ideas:
http://extra.wikitravel.org/blog/jani/rtw2007_barcelona
For cheap food, find a local restaurant without an English menu or like Maj says self-cater at the markets: at either, you can get a whole meal for the price of a plate of tapas on la Rambla.
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jani
Barcelona blog
As it happens, I just posted a blog entry on my first visit to Barcelona, which might give you a few ideas:
http://extra.wikitravel.org/blog/jani/rtw2007_barcelona
For cheap food, find a local restaurant without an English menu or like Maj says self-cater at the markets: at either, you can get a whole meal for the price of a plate of tapas on la Rambla.