Have you tried Chimarrao's Brazillian restaurant. It's behind the cinema across from Liquid Lounge near the corner of Marina Banus.
For under 10 euros you can eat as much as you want until you cannot eat no more. All the meat is fresh from Brazil and they carve it onto your plate at the table and they will keep on bringing it to you table until you say stop. Its nothing fancy... but good food.
I have never left there hungry... but always too full, cos the food is so nice. My favourite bit is the fried banana in breadcrumbs.
I took a mate there once (a pretty big guy) and he carried on eating for over an hour after we had had enough... and it didnt cost anymore than what we all had.
If you go there, dont have the menu... just go for the eat as much as you want choice. I go there all the time.
Regards, Paul
http://www.paulscottondesign.com