Last Christmas, a group of us spent 6 days on the lake. In Auckland, there are a number of clubs and Kayaking operations that are good. Julian Harris has a good description of the whole fiasco. Canoe and Kayak run a number of training courses and organise trips to various places around Auckland. Most of them seem to end up at the pub.
Cost includes all equipment and guides.
Great way to try sea kayaking without subjecting yourself to too much danger or overuse injuries. Be prepared to get wet mainly due to frenzied water fights. Riverhead trip includes a Smorgasbord lunch at the local pub. The first two are indoors and includes basic kayaking skills, rescue procedure, eskimo rolls, etc. The last two sessions are at Long Bay and are both full days putting into practice what has been learned in the pool.