well hostels and watching your consumption can help your budget, but it may be tight.
also, having a work permit for Oz isn't the same as having a job. you may get lucky, you may not. Also that time is the height of summer there, best to see about a job now, if possible, so you can roll into it.
I had a permit but ended up working for cash anyways for about 4/5 months (11 years ago tho and lots more poms now). Was easier.
Edit: Oz isn't so bad but remember that generally a reasonable job here in blighty will get you a lot more cash. Fruit picking aint great money unless you work hard. I've never really understood the people who fly to Thailand (e.g.) with no cash and then work for £5 a day or whatever in some arse end of the universe hostel - great to visit, not to live