for second hand cars, try: [URL="http://www.automall.com.hk/eng/main.htm"]
http://www.automall.com.hk/eng/main.htm
Euro cars more than about 5 years old are very reasonable compared with western countries.
fuel is around $15-16 HKD/litre at the moment.
There are also licence/registrations fees which are not cheap, though i can't help you on that as I do not own a car.
Unless you are planning to live in a more remote area, you don't "need" a car in HK, public transport here is brilliant and taxis are very cheap.