The spread in China is huge among Expats (even more huge on the higher end of the expat spectrum compared to the lower end of the locals).
The great thing is that with a comfortable Expat package (and those are rarer these days) and the willingness to not give into the Expat livestyle, you can really squirrel away some serious money.
I have had both experiences, living in China as a student (before it became fancy to do this), extremely cheaply on a shoestring budget in a shared dorm room, riding my bike across town, at a time when people thought you were nuts to do this and then years later as an expat, at the lower end of the expat spectrum with paid housing, allowance for taxis and food but not with an super cushioned expat package that most of my colleagues had etc.
I love the Chinese street food, so despite some occasional splurges (and quite a bit of travelling) I still socked away good money during that time!
At the same time I saw expats at the higher end of the spectrum (housing paid for, own driver, maid, housing decoration allowance, school paid for for the kids, paid flights home etc.) spending it all and still complaining how terrible it all was.
http://www.reddit.com/r/China/comments/22hb32/not_including_rent_how_much_do_you_spend_a_month/
The range is very large. I doubt the frugal posters are significantly less happy than the big spenders.
It's all about perspectives, often times the folks with the cushy packages are the unhappy ones, because they did not want to go to China in the first place and the company tries to "convince them with money".
It really all depends on your perspective, if you can embrace the opportunity.
Someday post-FI, I dream of coming back to the parts of China I REALLY love (the border provinces), teaching in a uni for one year or arranging a one-year visa back in the US, and just....chilling. Cleanish air, fantastic food depending on where you go, extremely cheap to live, and some really unique cultural experiences which won't be around in another generation. Of course that can be said of many parts of Asia, which is what's kept me here for over a decade.
Even previously remote places like Xishuangbanna are now ridiculously easy to get to. So the you have to go further and further to get to the cleanish air ;)
During the time I was travelling on a shoestring budget, Kunming airport was just a big tent, LOL! You had to ride the bus for hours and days to get to Dali and Lijiang and venturing into Xichuangbanna was like falling off the map.
Nowadays you have direct flights to Jinhong, Dali and Lijiang and air conditioned buses to move on from there.
Last time I went, we even paid a taxi driver to get us to Hutiao Xia, for not much more than the bus would have cost for two people.
It sounds more luxurious, but it's actually much less comfortable. Way more fun though, because he showed us stuff, we otherwise would not have seen and he took us to his home for tea and meet his family.