For the trip to Matamata we will take a bus for about 5.5 hours down there but it's only $22!!( There and back total=$44) Once back in Auckland however, most activities should be pretty close and a good walking distance or The Attic isn't that far from bus stations.
Auckland to Matamata-----------------> Hobbiton movie set;)
For activities just outside of Auckland the, Auckland Co-op taxi service (Blue Bubble) is to the rescue! Driving the greater Auckland area it also has a large fleet to minimize wait time. A little spendy but you shouldn't need to go to far anyway.