I got cheap flight from australia to New Zealand with jetstar think paid about 140 one way (incl taxes). Have found though that depends on what time of year etc. which obviously makes a huge difference!! Think the next cheapest air line was Air New Zealand.

virginblue is really cheap. house of travel and qantas air line. they're almost serve cheap flights and keep promotion.

theres not really cheap flights here, try www.virginblue.co.nz or www.expedia.co.nz or look on airnewzealand.com at grab a seat, sometimes they have cheap flights