Hi and welcome.
I think only you can answer that question - you have to decide how much you are willing to pay for the car and specification you want. You have access to the same websites as we do, so it will be a matter of searching cars sites in France. We have other members here from Romania, so I'm sure there must be C5s for sale in your country too.
Model specifications can be different and can change depending on the country the car is destined for to comply with various laws, so there is no simple answer. There is a site here that you can use to search for vehicles in the UK to give you an idea of UK prices and specifications, so you can just convert the currency for a rough idea - but as I said, cars will have different prices based on supply and demand of the country you are buying from.
Autotrader UK C5 Search Results
I've already put a random post code in for you and the year as 2012 - not many available as you can see.
