50% is often the number talked about in public while its much higher in reality as you are saying.
You can find even cheaper staff but you're still competing for talent. I can pay someone in South or East a premium against their market and still save big compared to an average salary in West.
This is ignoring any other benefits you have as employer in South and East. Try to fire or lay someone off in France - it'll cost you.
That wasn’t the part that killed the deal though. My employer’s real worry was around how hard they believe it to be to fire someone who isn’t doing well in France.