My flight is 7.00 am what is the cheapest way to go the airport from Quarry Bay, Hong Kong area?

As for your case, overnight city bus is suggested. But there is no direct bus running from your starting point to the airport. From Quarry Bay, walk to Mansion Street, King's Road to take bus no. N122 and get off at Diocesan Girls' School, Gascoigne Road, where you can transfer to bus no. N23 to the airport directly. The bus fare is 36.4HKD in total.