Tahuna Beach Holiday Park is huge, very close, and has a number of accommodation options from campsites through to chalets, give them a call at 0800 500 501 and tell them you're with the Ultimate Frisbee group. They MAY offer a slight discount, but they're already one of the cheapest Parks in the country. 

Check them out at:  http://www.tahunabeachholidaypark.co.nz/