YHA is worth joining, the digs I've stayed in have been tidy and cheap, and the membership is worth free wifi and a few dollars off the room.
I'm planning on staying there next month when I go a wee tour about, there are cheaper hostels, but worth paying the extra 10 sheckles so that you get a decent nights kip.
Did a wee three day stint in Wellington last month, was slap bang in the middle of town so plenty of pubs/restaurants and was a short walk from the tourist bits.
You got dates sorted out?
Give us a shout when you're in Auckland and we can grab a beer or three.