OzNos are just as good as the american nitrous systems; NOS and NX Express, the reason they're cheaper is because they are Australian built and therefore no import taxes. Also OzNos sell 'progressive' kits, so you can purchase a base kit then just add extra nozzles later if you feel the need. They have kits from 20hp - 800hp.
Anyhow, I'm sure they'll give you a better idea if you check out one of their retailers. This site is a N.S.W. retailer, but it'll give you an idea of what you're looking at, prices, and a product number to quote your local dealer.
http://www.ozrace.com