I was going to suggest what vwgal did. I spent a month in Marseilles and Paris while doing my Master's a couple years ago. I was able to stay LC very easily by heading to the Monoprix every few days - meats, cheeses, eggs, full fat yogurt, creme fraiche, great produce. Yum! You can also do the fast food thing - order a Royale and toss the bun! Plus it is actually very easy to find cheap good food in Paris. I was able to easily live on a student budget while there.