I'm hoping to get a soft count by the end of the week (13 Oct) and then go talk to some agents to see if we can do it even cheaper. Here's the basic outline of plan/cost so far:

Planeflight from LAX to Sydney and back, sometime in May: 950USD.

Sydney: nights in one of Sydney's apparently cool youth hostels. 24A$ a night. That's 18USD, probably for three nights. See the Sydney Aquarium, the oldest settlements in Australia, the Harbor Bridge and the Opera House, also the beach, if we so choose.

Spend night 4 on the train (or day five driving our rented car) to Melbourne. Train = 60USD. See neat stuff on the way. See neat stuff in Melbourne. Stay in one of Melbourne's youth hostels for three nights, spending between 2 and 3 days actually seeing Melbourne.

Take the train to Adelaide, City of Churches. Train is 60A$ (45USD), and will take most of the day (day 7?). See Adelaide for 3 days or so. Stay in Adeladian hostels for c. 28A$ (20USD) a night for three nights. Take the train from Adelaide to Sydney over the interior of New South Wales, I assume seeing things like kangaroos and such. Should take 24 hours to get from Adelaide to Sydney, so we can sleep on the train. Cost is appx. 175USD.

See anything we missed in Sydney, fly out on day 13 or so. Get back to Los Angeles four hours before we left Sydney.

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Total cost for travel: 950 (plane) + 260 (trains) = 1210USD.
Hostels @ 20USD/night, 10 nights = 200USD

Hostels + Planes and Trains = 1410 USD
(And that's marginally cheaper if we decide to rent a car instead)

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So, that's the cost plus activities (Sydney Aquarium will run us 25A$ (18USD)) and food, so... as little as 1500, depending on what you buy while we're there and how well we want to eat. And, of course, that's a rough number, but depending on how many we get, we might be able to bring that cost down.

1500USD to see Australia? Sounds pretty good to me. If you want in, let me know and we'll figure out dates.