I'm on Centrelink + using my savings my savings but I might need to get a job eventually.
Yeah I'm pretty much in the same situation, getting by pretty well so far. I'm finding that I usually have to resupply on groceries every fortnight or so.
The rent does vary for each hall. B&G and Fenner Hall are the cheapest ones. The catered halls are expensive.
http://accom.anu.edu.au/UAS/977.html is a good start, where it'll take you to a link with the prices for each residence, and also a link about accomodation bursaries. Read everything on that site basically
Each hall also offers bursaries for rent I'm fairly sure, they should be listed somewhere on the accommodation website. I don't know about the other halls, but Fenner Hall also has a PhB busary for half-price rent.
$20,000?
The new Tuckwell scholarships that they're starting up this year gives 20k a year.
There's more scholarships than that,
http://students.anu.edu.au/scholarships/ug/ is a good start for those. There's a variety of scholarships for 99.70+ students too. That page lists all of those. Don't quote me on this, but I'm not too sure if there's a specific PhB scholarship anymore, but I'd imagine a lot of PhB kids would be eligible for one of those merit ones anyway.
There's also organisations/foundations and what not that offer scholarships that you'll want to look into, your careers teacher or someone at your school might know stuff about those.
How you get to spend scholarship money is up to you I'm fairly sure, most of them will detail how you get the money (whether it's bulk payment, or applied directly to your rent etc.)