After checking in garages and stores, we went after low-priced tyres on specialised sites: [...]
-pneus-online.fr [...]
All of them offer highly competitive prices. Savings start at 20% (for small sizes) and go up to 50% (for large sizes). The only drawback, which is a considerable one, is that you have to find a way to get the tyres mounted yourself. Very often automotive centres as well as dealerships balk at working with tyres they didn't sell you. At a service station, things are often easier.