What should I do to become a pilot for skydivers, in France? What are the steps needed to become a pilot that can transport skydivers?
I'm more specifically interested in the situation in Europe, France.

I would expect lessons / certifications, then more certification to accept passengers, then more certifications to be allowed to carry skydivers and let them jump. Also, medical examination, books, insurance, fees...  

How much would it cost?
I'm more interested in the money amount spent usually observed than the theoretical price. I have a day job so I won't be able to easily spend all days of the week at the airport.  

How long should I expect until I'm certificated?  

Then, how often should I fly to stay current. 
Obviously, there is the issue of practicing enough to be safe and the legal requirements to be allowed to fly with passengers.

I also expect to be required to be certificated with a specific level for the skydiving. Bonus points if you can answer that too.



I have seen this question about how much it cost to learn to fly, but it is less specific than my case. Still, many interesting points in its answers.
Short answer: you need a commercial pilot's license. The drop zone will provide the extra training, it takes about a day (I worked at a skydive center for 10 years)

However, since you seem to not have any kind of pilot's license right now (or you would know this already) I will add that it isn't a full-time job at any except the busiest drop zones. Our pilots usually worked for a couple of years to build time and then went on to other aviation jobs. During those 1-2 years they had other income - flying for us was mainly a way to log flying hours without having to rent aircraft.