Miami is one of the few American cities where the cheap food is also the food worth travelling for, which makes a low budget much less of a compromise than it sounds.
The ventanita is the whole system. A walk-up window on the side of a café serves colada, cortadito and café con leche to people on their way to work, standing up, in a couple of minutes, for small change. A colada comes with a stack of thimble cups and is meant to be shared, which is the most Miami thing on this page. There are windows all over the county, not only on Calle Ocho.
Counters beat tables. A Cuban sandwich, a croqueta, a pastelito de guayaba or an empanada from a bakery counter is a few dollars and better than most sit-down lunches on a tourist strip. The Latin bakeries in Little Havana, Hialeah, Allapattah and along Bird Road do this all day.
Lunch specials are real. Many neighbourhood restaurants run a weekday lunch plate at a fraction of the dinner price, and it is the same kitchen.
Eat where the language changes. Cuban, Haitian, Colombian, Venezuelan, Nicaraguan and Dominican cooking are ordinary weekday options here, not a themed night out, and the version aimed at residents costs half the version aimed at visitors.
Two places to spend nothing on food deliberately. The picnic blocks in the free day plans — Bayfront Park downtown, South Pointe Park on the island. Note that alcohol and glass are prohibited on Miami Beach's city beaches, so a beach picnic is food and water only.
Carry small cash. Most of the city is cashless. Ventanita counters and market stalls often are not.