Auckland Airport: Waikōwhai is an Auckland suburb, not a West Coast town with its own airport. For the cheapest sensible public-transport route, take AirportLink/route 38 to Onehunga, then the 68 bus toward New Lynn via Hillsborough/Waikōwhai. Allow roughly 55–80 minutes, depending on the connection, and budget about NZ$10 or less with an AT HOP/contactless fare; it is much more logical than taking an airport coach into the CBD and doubling back. With heavy bags or a late arrival, take a taxi/rideshare directly: usually 25–40 minutes outside peak traffic, roughly NZ$55–85.
Waitematā Station (central Auckland; still commonly called Britomart): From central Auckland, use the rail network to Onehunga where services suit, then connect to the 68 bus for Waikōwhai. Allow about 45–70 minutes door to door and roughly NZ$5–8 in public-transport fares. There is no useful intercity station in Waikōwhai itself; this is a residential, hilly suburb rather than a standalone visitor city.