Recently i have been food shopping across the border in France (Divonne, Gex, Ferney, Annemasse), and I noticed some big price differences on some basic items like bread, milk, washing powder and so on between different chains or even different shops of the same chain (Intermarche, Geant, Carrefour, Casino).  Some prices were even more expensive than Switzerland.  It wasn't a scientific study so i won't express an opinion as to where is cheaper.

Has anyone got a long experience of the French supermarkets and can anyone give guidance on where the best value for money can be found.

What about the french street food and vegetable markets.  Again i see big price differences even in the same market.