Here is my first recommendation:
The 11th Street Diner at 1065 Washington Avenue. Definitely under ten dollars for most items in the menu. Breakfast, burgers, sandwiches, salads, desserts. It’s open 24/7, but of course the late-night crowd can be a spectacle. Did I mention that they have a full liquor bar? You didn’t mention your age? [:D]
There are two David’s Cafes One is on the Lincoln Road pedestrian mall.
Click here for info: http://www.davidscafe.com/
As wanderingjew suggested, Puerto Sagua 700 Collins Ave.