I would make a list of everything that you are going to spend money on. Budget a little too much for everything. So if rent is 100 - 150 Budget 150 or 160. Work out all your rent for the year. Then add in power, gas, phone and water (if the place charges water). Be a little generous. I would do it all in pounds first and at the end transfer it over.
I would give about $80 a week for food. I mean I have lived on much less but you don't know how much everythign is going to be. Remember to put in transport (probably will be at least 15 pounds a week), as well as text books etc.
If you plan on working for your money I would have at least 2 months back-up that you can survive on while trying to find a job. If you plan to work in a a coffee shop remember some places require courses. Like here in NZ (I just moved here) you need a Food Prep Cert. if you want to work in a sandwhich bar or something, and a Liquor Cert. for bars, and the Liquor one costs $450 so if you are going to do that be prepared for costs like these.
Also remember you can take over very little and its usually cheaper to buy a lot of the basic things again rather than pay for transport so I think you should leave at least a few hundred for that.
When you have done all that add in your airfare, tally it up and convert it to AUD. I would then add a 10 - 20 % extra 'buffer zone" then try to save that.
Also look into how easy it will be to find accommodation. If you are going at the beginning of the academic year it might be difficult to find a house. I would allow for at least a month in living in a hotel/hostel. Also remember you may be required to sign a 12 month lease, and pay up to six weeks bond and/or rent in advance.
The Thorntree Forum (Lonely Planet) is a travel guide but lots of people ask questions about moving to places, like living costs etc. and you can find out the truth from people who live there.
Good luck
