Yes you can get cheaper detectors, keep in mind that if you don't get off to a good start with a good machine you will lose interest very quickly, you will need to invest time into your purchase and there is no point getting a cheapo detector learning it and still not getting results. Sure some of the cheapo detectors are better than others but why risk it, start with something tried and trusted, if you decide you don't like it then it will be easy to sell.
But if your in the Dunedin area go cheap, cheap as you possibly can. That way there will be plenty for me to find after you've been there *;^)
F2 - F4 Solid choice
http://www.puiakisupply.co.nz/