and if there is no new available, only used, that actually makes the price even higher (I know that sounds counterintuitive but yeah used equals more expensive).
Since you're in NZ, maybe that's the case because it's someone who doesn't have a discount shipping rate, but
I take that more as a sign they're out of print and are scarce. But if a new one shows up, it'll still end up being more expensive. e.g. just looking at the Blu-ray for The Velvet Vampire, it's currently $365 (USD) new on Amazon (us), and $299, used. (The DVD from a different distributor, is $10, making it probably the biggest discrepancy I've seen between a DVD and a Blu-ray in terms of price).
In those cases, I'd suggest, unless it's a movie you must have, hold off, and hope someone does a re-printing of it in the next 3-10 years. I've seen movies that get into the multiple of hundreds of dollars become normal priced once a new printing happens (often from a different DVD label that gets the rights).