Please recommend casual in Chandler St
The Chandler Inn is in the South End so if you search for restaurants in that neighborhood, you should find plenty. And for what it's worth, most of Boston can be walked from there in about 20 minutes or so.
Delux on the corner of Chandler and Clarendon (one block away) is extremely casual and quite eclectic. Decent food, cheap prices, cash only.
Giacomo's (another cash only spot) on Columbus has good Italian/seafood.
Pops on Tremont St. would be another good option for you.
You're in luck in that the South End had a slew of recent openings of more moderately priced places: Pops (gussied-up comfort food in a very pretty setting), Rocca (cuisine of the Italian Riviera), Coda (fancy pub food), Gaslight (classic French brasserie). In the moderate range, I also like J.J. Foley's (a hundred-year-old saloon with above-average pub food), The Franklin Cafe (cool bar with above-average American food), The Dish (good grilled pizzas and New American entrees), Masa (Southwestern), Toro (fun tapas place), Orinoco (tiny, excellent Venezuelan) and Petit Robert (lively French bistro). Lots of good options for patio dining, which is lovely at this time of year.