Petrol or diesel?

If you don't need 4 wheel drive, just a good set of tyres and maybe some type of locking rear diff.
http://www.ssangyong.co.nz/actyon-workmate/ (2wd, tyre, rims upgrade) (2 litre diesel and 5 speed auto) http://www.isuzuutes.co.nz/utes/ls-double-cab/ (3 litre diesel auto2 wd) Also check out http://www.ecuchips.co.nz for diesel tuning for economy
If your route has the blind corners that can be foggy in winter; a van would be a lesser option.

our postie has a Daihatsu sirion 1.3 manual, been here 3 years, rural run, gravel roads. cant imagine there would be much cheaper than that!

Ah diesel!

The outlander phev used 1.9l/100km in the combined cycle test. This was done starting with a fully charged battery so I would have done the first 60km on battery power alone. For the rest of the distance the petrol engine would be running. I'm not sure exactly how long the test distance is but it's quite short, someone here should know. So once the petrol motor kicks in it's actually not that economical. NZ Autocar tested one and from memory once your battery's flat it averages about8l/100km so it's really only viable on short trips with mains charging in between. For the OPs use a diesel outlander would be far better than the phev version.

Actually check out the ad for the new Citroën c4 cactus, good fuel economy right there!