"I do wonder if the cost of French wines is largely down to prestige rather than taste."
I would suggest that the French really do make world class wines, they have the experience and the know how.
BUT, you have to know in advance what you want, expect, for what occasion, with which food etc....
Not all French wines are good, far from it, most of them are pretty poor. But, when it comes to the top class bottles then there really is no question of prestige, it all comes down to what floats your boat.
I have drank some very expensive wine, even the same wine on different occasions ( read : with different food) and the taste can change drastically.
I have also drink excellent, first class Portugese, Spanish , Argentinian, South African wines which are easilly on the same level as the French Wines. Even this week I was in Marocco and was very pleasantly surpised to drink some very fine local wine there.
The French have prestige because they can constantly make good wine, the selection is enormous and the massive regional choice ensures that there will always be good French wine..
As far as price goes, forget it, it is not an indication of quality.
Golden Rule : never buy for the ticket buy for your palate. If you like it then it's a good wine, if you don't , try another bottle :-)