I'm just a private pilot for my own amusement, but I know several French airline pilot wannabees. All of them have spent serious money getting a "frozen ATPL" - I don't know how much but I guess the figures in earlier responses are accurate. This is money they have borrowed that will eventually have to repay.
Then it's a question of hanging around waiting for someone to offer them a paid job flying. That implies getting a type rating, which is further expense. One of them (who was my instructor for a while) has now got a job flying bizjets for a company in Geneva. The other three are still waiting.
Bottom line... you have to spend lots of money, which unless you have wealthy parents implies taking on a serious debt burden. Then you have to wait and pass a lengthy poorly-paid apprenticeship flying bizjets or working for Ryanair or Wizz, before you finally get a decently paid job with a decent airline.
All that said, the people I know love it and are absolutely convinced they are doing the right thing. I met one guy who is now flying for Air Caraibe and loving it, but he sent several years at Ryanair which he said you just have to like a doctor's internship. He certainly didn't seem to have enjoyed it much.