Of course, it is a wide field, but for Germany the navigation devices by Garmin or TomTom are probably best.
If you buy one over here, it is standard to have maps for like two dozen European countries with lifelong map updates at no extra cost. I have also seen some that include map (with free lifelong map updates) for the "world".
Of course, the devil lies always in the detail: "Lifelong" normally means something comparable like with Windows OS - at some point the devices are no longer produced/supported. But by my experience, they break down / the battery is dead and too expensive to replace etc. before you run into problems regarding the "lifelong" updates. Then, one would be well advised to scrutinize, what "world" means if you buy here. Who knows if this would include countries like Afghanistan, Micronesia - or Australia?
You'll find relatively simple ones for 100 Euros. Mid-price is 150 to 180 Euros. High price-segment would be 270 to 350 Euros. The more expensive ones, you can connect to your smartphone which will enable the navigation device to draw on more precise traffic info (but if you use a phone contract from Australia, roaming fees would likely be a killer). Many use smart-phone apps instead of dedicated navigation devices. These work well, but of course draw on your data allowance if you don't have a flatrate (and might be expensive due to roaming in your case).
This is just a rough outline from what I glanced over in adds of newspapers. I did not dig deeper into it for quite some time as my car has a built in one.
As for where to buy one over here: Every larger electronic market has them. Or you could buy via Amazon, though I am not sure they will deliver European devices to Australia.
Then, you should inform yourself if there are any "specialties" to be considered. It has been a couple of years since I have been to Australia. But for some reasons (that I have forgotten), European SIM-cards for a cell phone did not work in Australian cell phones. What we did was bying two cheap cell phones in Australia with Australian prepaid cards.
von Marwitz
