There are many posts about expenses/costs at various hospitals, which vary greatly depending on your situation.
When you go private, you have to keep in mind that you are fully responsible for all the fees, including worse-case scenarios, which can cost quite a bit. I also hear that if you choose to go 'fully private' from the beginning - even if you have an emergency and have to go to Queen Mary (where the NICU is) they charge you a higher 'private' fee. Whereas, if you choose to deliver there from the beginning, everything is charged at 'public' fees. (see QM fees here:
http://www3.ha.org.hk/hkwc/ppi/downloads.asp#fees)
If you are concerned about costs, I would think that planning to deliver through a public hospital, but supplementing with some private prenatal care might be the way to go, that way your costs can't get too out of control.