I've heard that living in Guangdong is very expensive, compared to many other less well-developed areas of China

Interesting points, but in terms of GDP it is actually behind provinces like Jiangsu and Zhejiang. Even Shanghai for it's size, is considerably better off. Not saying I would work in Shanghai, but one only has to go to the countryside in Guangdong to see real poverty, or Luoding as was previously mentioned.