As a guide, my private car is an Opel Zafira 2.2 (I believe my tax bracket is 1.6 - 2.5 litres)
Approximate Monthly costs:
Parking Home 700HKD (relatively cheap because I live in NT, expect to double that or more nearer town)
Parking Work 500HKD (because I ride my bike to work when I can)
Parking Other 300HKD
Petrol 1500HKD
Tax 500HKD
3rd Party Insurance 250HKD
MOT/Servicing/Tyres/etc. 300HKD (obviously this is an estimate but I think it's fair on a used car and I also have a bit of local knowledge which reduces these costs for me, I expect a newbie will pay more.)
Depreciation (obviously depends on your car but you must consider it of course)
I have two kids and tried living without a car for about a month, I hated it! I believe having a car generally makes life easier and gives you a lot of freedom. Public transport is very good here and very cheap but nothing beats the comfort and convenience of your own vehicle!!
That said, it is an expensive luxury and would be a lot more expensive in Kowloon and even more so in Hong Kong...