Mimosa : you’ll find wonderful fat-laden French food in this friendly restaurant on Rue d’Argout in the Bourse & Grands Boulevards area (metro: Sentier).
Within walking distance of the Louvre, there is Le Petit Flore (Rue Croix des Petits Champs, between the Louvre and Bourse). An unpretentious little restaurant that’s popular with the residents of the 1st arrondissement, this “pas cher” (lit. “not expensive”) eaterie proves there are discount restaurants in the center of Paris.
Just east of Bastille, there’s the Paris Main D’Or (Rue du Faubourg St Antoine, metro: Ledru Rollin) which serves home-made Corsican food. The food here is very tasty, but the waiters and their high energy banter helps draw in the customers.
Across the river, Le Petit Saint Benoit : on Rue Saint Benoit (metro: St Germain des Pres) is like a step back in time - don’t even try using one of those new-fangled credit card things - but, fortunately, their prices are also an anachronism. This inexpensive Paris restaurant in the Sorbonne area is a great place to have dinner as you can see St Germain at night with a romantic walk afterwards.
West towards the Eiffel Tower is Le Sept in Rue de Grenelle which is one of my favourite inexpensive restaurants in Paris. Its cheap Mediterranean menu (e.g. Greek salads, pastas, fish) is just the thing if you’re looking for lunch in the 7th arrondissement .