Many French supermarkets have a 'foire a vins' at the moment and there are some bargains to be had. Take a corkscrew and glass with you so that you can try promising bottles in the car park. You can check what is in the promotions on their websites. Personally I'd get a few bottles of Pomerol and Margaux, they are a bit pricey but excellent with rare roast beef. Lidl do some good and very cheap Spanish wines. 'Batturica' is I believe much cheaper in France than UK.