In France, you don't have to give a tip normaly, I give a tip when services are much than I think it should be.
Prices start about 10 euros, one dinner with wine in a basic restaurant is about 15 euros, You can find lots differents, prefer traditionnal food with locals speciality it will be more quality for the same price. Small Budget should try restaurant in places that aren't Touristics, every region have speciality which can be very different from one place to another
Cheapest Supermarkets are biggest, so cheapest are Auchan, Carrefour, Leclerc, Intermarché. There is others discounter like Leader Price, Lidl, Neto, it's about the same price than in others. Often they are open from 9h to 19h, more late in big city. Often some really small shops are open very late
Local Specialties ...