You can take the A41P from the airport to Ma On Shan plaza, then get the 299 to Sai Kung. Total trip time of less than 1.5 hours. You can also take MTR to Diamond Hill or Choi Hung, and then a mini-bus to Sai Kung. Probably more like 1.5 hours plus a little. Driving your own car is about 40 mins. I suggest taking a taxi and scrap the car. Should be about 200-250 each way, and you don't have to pay for parking. Hope this helps.
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