Cheapest way from Pacific island hotel to HKIA airport?

Here is my way at the lowest price:
walk to Queen Street, Connaught Road West bus stop within 10min to take bus no. E11 to the airport. You need to get off at the Passenger Terminal Building, Cheong Tat Road. Then follows the boards to HKIA. It takes around an hour and the cost is 21HKD.