Cheapest and quickest transport option from Auckland Int Airport to Auckland CBD and back in a day?

I'd say Airbus Express is your best option. It's way cheaper than a taxi and it runs every 10 minutes from the city to the airport (and vice-versa). http://www.airbus.co.nz/

Yip Airbus Express is your quickest and cheapest option. $26 return http://www.airbus.co.nz/ Unless you are travelling with someone else, because a taxi is about $60 one-way, and would be quicker. If you just want cheap you can take the orange Manukau 360 Airporter Bus to Papatoetoe train station and take the train into town from there.

since we are the only large city that does not have trains running from the airport to the city, the best transportation/s would be taxi, buses, i think you can get shuttles there, or you can hire a car for the day. the best taxi company is Green Cabs. Ph. 0508 4 47336 (4 GREEN) or www.greencabs.co.nz you can easily hail a taxi at the airport because there are always someone there (all companies) Shuttle to AKL CBD: http://www.shuttlebus.co.nz/prices.html (scroll down till you find 'Auckland City Centre) Car Rental: http://www.rentalcar.co.nz hope this helps :)

The train out to Papatoetoe is cheap, then Manukau Airporter bus from there to the terminal, but it's not as quick as the Airport Express Bus there and back. Just make sure you get the CITY bus, not inter-terminal by mistake.