The new Z10 Buggy has different front suspension, rear suspension, shock towers, chassis, and radio tray. The Z8 can be converted for 259.97 (this consists of 3 kits --- front, rear, and chassis/radio tray/towers). If you add the Z10 Body it would be 286.96.
A new Z10 sells for 439.99 and will give you all new parts (diffs, bearings, body, etc.)
If your buggy is in good shape as far as bearings, outdrives, wing tower, diff cups, then it would be ok to just convert it. If your buggy has some wear and tear (mine has 3 years worth) then it would be better to invest in the Z10. A LOT of R&D went into the changes to the new Z10. It is the next generation of Z-CAR.
I will have to check and see on the shipping to New Zealand. Wouldn't think it should be too much though.
Jonathan Jenkins