Have a look at ADV website. Plenty of bikes for sale, but you need to keep your eyes open for the bargains under 3k. Inmate Qute said he had a Dominator for sale for 2.5k (not advertised).
Gumtree is also a good option.
Postie bike will take you most places, but you have to be mechanically inclined if you're planning to go remote/outback. And you'll need extra fuel- roadhouses are upto 300km apart in some places. Some of the 'less traveled' roads, you'll need fuel ranges of 600km or more.
Renting is an option, but as far as I know it'll cost you around $100/day for the cheaper options. The longer you plan to tour, the more cost-effective it is to buy.
Just remember on top of the purchase price is licensing/registration fees and insurance.
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Squily
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