There was someone on e90post selling BMW mobility kits (in Canberra) for $180 last week. Don't know if that's cheap or not - but if you're after a quick solution - And in Canberra!
Also, don't know if you know but the coast road is great now! Back in the day I always went inland, but the last few trips via the coast were heaps quicker.. I was in a 73 911 so didn't want to go 'outback' just incase. And will continue to go that way from now on..