I have a BOC MagMate180P welder, has done me well so far. No longer available I don't think. You can buy a 150A version though:
http://www.boc.co.nz/shop/en/nz-boc-ind ... agmig150-p not sure if +GST or not. But I find mine great, easy enough to use. No experience with other cheaper welders so can't comment on others. You can buy cheap welders, but you do tend to get what you pay for. If you plan to keep it long term, and use it quite a bit, it's money well spent.
I've used mine for car panel welding (even some panel which was about 0.5mm thick, right up to welding 12mm reinforcing rod together to make a table for someone. Realistically, 150A would have been fine for those jobs, it wasn't available when I got my 180A welder.