Why is Costco's butter half the price of NZ supermarkets prices?

If you're a baker, or just like to smear it on your toast in the morning, you've probably noticed the price of butter steadily climbing in recent months. But there is one place where prices haven't risen so much - and where people can get butter much more cheaply than in other supermarkets. It's Costco, in Auckland's north-west. Money Correspondent Susan Edmunds spoke to Lisa Owen.