I'd like to assign a unique IPv6 address for each user of my service. Since I'm in Australia I looked to APNIC but their pricing is a bit intimidating for a side project. I'm primarily after stable addresses so that my users never have to reconfigure anything if the underlying infrastructure (Vultr to start with) changes. What options should I be looking at?
Well, no such thing as stable addresses since you don't really own IP addresses, you are leasing from RIR.
But, if you are fine with APNIC allocation, see if RIPE PI Allocation is sufficient for you, they are much cheaper(RIPE charges $50/yr), add some LIR cost, total would be <$100/yr.
Yeah I'm aware you don't really own IP addresses just as you don't really own domain names. In both cases there is degrees of stability you can expect though. I'll look take a look at RIPE, thanks.