Allston and Chinatown have their adherents as go-to neighborhoods for inexpensive, high-quality restaurants of every stripe. But in East Boston, adventurous chowhounds have uncovered a treasure trove of excellent, dirt-cheap Central American, South American, and Italian-American restaurants, not to mention a Styrofoam box full of fine blue-collar shore food. Want to learn where Boston's high-end chefs are getting their ideas for their next great $30 entrées? Hop on the Blue Line, friend, where you can experience the real deal, usually for under $10.