Thank you all so much for your insights! That is exactly why I signed up to the forum, I knew there would be folks out there in the same situation as us.
We are located in Tocumwal, on the Murray River, so although some of those ads look great, we are really not prepared to travel to the other end of the country to find one (good point 'tryagain').
We are looking at Aussie-made predominantly because so many people have told us that Aussie made has a far better build quality than the cheaper Chinese imports. We know we could buy a new Chinese one with our budget, but we want to reliably tow it (with 4 kids on board) around the country on holidays with some degree of confidence. We have looked a few and you can always pick out the Aussie-made ones. They also seem to hold their value pretty well.