What kind of mobility do these people have? Could they choose to move to somewhere in rural China and get something of decent size?
Most people actually would rather stay in HK to take advantage of the better education and healthcare system for their children than moving to China for a __slightly__ more affordable place. HK is also a much safer city to live in. The food is generally safe and the police is fair and professional.
Commuting between HK and China is also a big problem. Most jobs in HK are in the urban areas in HK, commuting from Shenzhen or elsewhere to those areas daily can take a huge chunk of money out of their wages, let alone the 3-4 hours they have to spend commuting.