I have a Tom Tom One but it doesn't have NZ maps.  Buying the maps at approx $130 wouldn't seem to be very good value, I'd rather wait and save for a new unit.

Is it an option to buy them second hand, perhaps off of someone with a faulty or old Tom Tom?

If so, what should I be looking for in terms of format? Is it just a bunch of files or do they need to be loaded in a special way to work? What are the pitfalls?

Any other options? Please PM me if you've got any offers!