I have to agree with what you are saying and I am an ex property owner. However, I also see the other members points of view as well. If there is a cheaper alternative out there, please post it I have no objection at all unless it's breaking forum rules, in fact I would love you to post it because at the end if the day like you said a lot of people don't have $600 plus per week.
What people also need to realise is that short term rentals are expensive in Australia. I've currently got my mum staying in a hotel close by its $380 per night and Rob is in another hotel which is a backpackers and that's $99 per night. So when you compare this with the $400-$600 per week and you are getting a full house rather than a hotel room it's a no brainer.
Personally I don't like gumtree I have seen too many people scammed out of money and people paying for a property that doesn't exist. At least with members on here a lot of people have already used them and no they are genuine, if ever we received an inclining of something being a scam it would be removed immediately along with the member.
This is a forum we are all entitled to our opinions whether others agree or disagree should not matter.
Please don't forget to post the info for the alternatives I'm sure there will be many who find this useful. If you have photos of it that would be even better.