The Orbi RBK50 (top model) mesh wifi system is currently $335 shipped & sold from Amazon Australia at the moment… Quite a good price, especially when it is still being sold for $528 at Officeworks…
The lowest ever price this one has sold for (on Amazon AU at least) is $329.95 on December 23, 2019 - it went out of stock quite quickly then as well..
I own one of these myself, it has been rock-solid and as a result of getting it there are literally no black-spots at my house.
However, do keep in mind that a WiFi 6 version of the Orbi is supposed to be released in Australia in Q1 2020 - it's already been released in the US, but for $700 USD, so expect it to be quite pricy. Plus, from what I've read, until literally all your devices support WiFi 6, and it becomes mainstream there's not much point in becoming an early adopter.