The buying power is roughly 5:1 everything included. In other words, if you are making 100,000USD in the LA today, you only need 20,000 USD to maintain the same quality of life in any cities in China except the big four. If you are making 20,000 USD in ChongQing, I am confident that you will not move anywhere.
If you are approaching 40 and still work as a coder, better pack up and go to China as the red slip is coming any way.