Transport from Cosmos Hotel Wan Chai to Hong Kong Airport.

There are 5 of us in the family and we figure that if we take a taxi to the airport, we would need 2 vehicles. Besides, we read somewhere that we have to pay $5 for each piece of luggage. We probably would have quite a number, big and small, after all the shopping. Would really appreciate your advice on the most cost-effective way to get to the HK Airport from Cosmos Hotel in Wan Chai, in the afternoon. Thanks a million!