First of all you need to go to transport department, fill in the form, book and pay the fee for the written test. Once you pass the written test, you get a temporary licence in order to do the driving lessons.
You may call this guy: KONG, FONG NAM (+852 9055 1305). I did a couple of lessons with him last year, HKD 300 for 45min class. Private car with manual transmission. Bear in mind that if you do the road test with automatic transmission car, you will be restricted to drive this kind of car only.
According to my research last year, this is the cheap way to get a driver's licence here in HK. I remember there were some instructors with automatic transmission car charging HKD 290 per class. So you may go through the driving instructors and ask for information.
Good luck.