A lot of times, I still eat at table serve restaurants and can hit right around the $20 mark - plus or minus $5. Obviously depends on what you order. But places like Rainforest, T-Rex, and House of Blues all have very large portions, and have sandwiches, salads, burgers, and appetizers right around $20 or less. Similar for City Works and Splitsville. Your total bill, with tips, or if you get drinks, will likely creep up near $30 - but Polite Pig won't be too far off either if you get one of the BBQ smoker options.
If I really want to keep it cheaper - like food for $15 or less plus a drink with a total tab around $20, then it's usually DLuxe Burger, a sandwich at Polite Pig, Chicken Guy, Pizza Ponte, Cooke's; in an outside-the-box idea, consider a walk over to Artist's Palette at Saratoga as they have some pretty decent sandwiches and salads...it's only a boatride away, or a 1/2 mile walk from Rainforest.