What areas to choose to buy property at a reasonable price in France?

The map of French property prices always looked like this: the city of Paris first, then greater Paris, then the other big cities - Lyon, Nice, Bordeaux - then the Ile de France, and then if you skipped the middle and went right down to the bottom, you'd find two big areas of cheapness, on the periphery in Brittany, and right in the middle of France where the whole of Limousin, Auvergne, and Berry were good value.