For a delightful budget lunch in the 6th, go to Cosi, on rue de Seine. The midday line at the door speaks to the value, and the hand-written chalkboards inside illuminate the fare: hefty meat, cheese and veg sandwiches on warm focaccia, huge salads with market-fresh ingredients, creamy soups like zucchini/fennel and lentil curry with ginger — with prices starting at 5€.
Order, pay, and pick up at the counter on the rez de chaussée, then carry your tray upstairs to two sunny rooms overlooking the narrow street.
A neighborhood treasure! Cash only, free wifi, open daily noon to 11pm.