My sister-in-law and her husband has no mortgage. Like many families here, her husband's family helped with the purchase of their apartment.
Monthly Expenses that I know of ...
500 RMB for household fixed costs [ telephone, electricity, water ]
500 RMB for household fixed costs [ for her parents' place ]
2,500 RMB for food
They're not big spenders but cost of living adds up. They also have a 2 year old son.
David has it right that there are more poorer people than middle class. The gap is even getting bigger. In Kaiping, a typical villager grows his/her vegetables and sells the excess amount on the street markets for spending money. Every unused plot of land is utilized by a vegetable garden. The single thing I admire about the Chinese is that they enjoy whatever life they have despite their income level. They always have plenty of food on the table and are very warm hosts. Other than a television, mah jong tiles & playing cards, they have no need for anything else to occupy their leisure time. Westerners may make more money but they spend more and are probably unhappier because most want to keep up with the Joneses. The credit/debt system will be the doom of the next generation of Chineses.