[Alfajay]

I have no idea of how much of a premium/discount to place on it due to:
- it is rare (750/101's were never sold new in NZ, true?)
- the steering wheel is on the "wrong" side for NZ roads
- being a Yank, I know nothing of vintage car values in NZ

So, ignoring all of the above, if it were for sale here in California, the rust you describe would suggest a pretty deep discount. I feel that dretceterini's number, $3,000, would be near the top of the range for a complete car with what sounds like pretty serious rust issues. The rusted trunk floor doesn't sound that bad (they all have that), but the "rear valance, and r/h A pillar base and inner kick panel" sounds pretty severe. And of course, once you get the paint off of it, you will find a LOT more rust.

As Pathung wrote, pictures would help. Also mentioning whether it is a Veloce or normale, and the condition of the interior.