This is very useful. More details:

According to this page,

City World Cost of Living Index

Beijing 95.6
Shanghai 90.4
San Francisco 84.9

How does this compare to average US cities? According to this page (http://www.infoplease.com/ipa/A0883960.html), the cost of living index for San Francisco is 177. So translating the world cost of living index to US cost of living index, then

Beijing 199
Shanghai 188

In other words, if you make US$100k in an average US city, you would need to make US$188k in Shanghai, and US$199k in Beijing.