Numbers I work with are ~45k for a senior software engineer in Hungary, Spain, Italy, Greece vs ~85k in France, Germany, the Netherlands. Fully loaded cost (tax, insurance) adds about 20-30% on top in West. South and East are considerably less.

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.