Driving at night on a round Australia trip is unwise. If you really think that you'll need to do so then you would be far better off choosing a shorter route & enjoying a more relaxed (& safer) pace. There is no 'badge of honour' for circumavigating the country just to have done so. Why not do half a lap over the same time period?
When money is tight spending on lights for the trip makes little sense in my book, they would be way down at the bottom of my list ....if they were on it at all.