Apparently 20-30% cheaper than places in CA for most things, but to buy an apartment it's more expensive.
Wages are 75% or so cheaper in Shanghai, but purchasing power is 66.36% lower too... http://www.numbeo.com/cost-of-living/compare_cities.jsp?coun...
Seriously? The mean household income is US$4,700/year [0] (nominal conversion). Your link claims it's $12,000/year for an individual, but if you investigate further, that's the mean of the high-income expats who visited that English-language website about international costs of living and filled out a survey. The very existence of this large expat population skews the mean; I'd guess "typical", median wages are a lot lower than $4,700.
[0] "Average annual income for a family in 2012 was 13,000 renminbi, or about $2,100. When broken down by geography, the survey results showed that the average amount in Shanghai, a huge coastal city, was just over 29,000 renminbi, or $4,700, while the average in Gansu Province, far from the coast in northwest China, was 11,400 renminbi, or just under $2,000. Average family income in urban areas was about $2,600, while it was $1,600 in rural areas."
http://www.nytimes.com/2013/07/20/world/asia/survey-in-china...
Income of $5000 would be approx $7700 PPP. Not exactly extremely wealthy by developed countries standard...