If you are going to do something major with the electrical fittings in your home, such as change the entire wiring or restructure everything such as when you renovate your house, then you need to tread very carefully. There are several electricians in your area, and electrical companies as well. The competition is good for you. Find out as many companies as you can, and check out their references and credentials. If you think they are good, then you should give them a call and talk to them about what they can offer.
They will usually send someone over to come to your house and then check what you exactly need. They will need to see the exact work that has to be done, and you have to explain to them as precisely as possible. Once that is done, they will come up with a quote and then you can decide whether you want to go ahead with it or not.
You must not depend on one quote though. Ask around for as many quotes as you can get, and you will find that the price varies heavily as well.
However, that does not mean you should go ahead with the cheapest. Electrical work is tricky business and you do not want to land with cheap wiring and faulty fittings that could wear away in no time or, more dangerously, cause accidents such as electrical fires.
You should start with a reputable company such as Electricien Guyancourt first and then look for other options as well. Do not think that the bigger companies are pricey; even if they might quote a tad bit higher, they will provide you and your house with a very safe and professionally-done job that you will not have to look at for a long time in the future.