Daily budget food & drink 5 USD - 30 USD. Accomodation 0 USD - 50 USD. Whilst you may be happy to rough it you'll appreciate some creature comforts (if only a bunch of
s) once in a while hence the wide spread. Re the bush camping to paid accomodation ratio, I doubt you'll break the 50 percent barrier. Bank on paying for your accomodation in 75 percent of cases.
Other costs are: Fuel, Oil changes, Insurance, Vehicle maintenace, National Parks, Heritage Sites, Guides, Ferries, Border fees.
Re money I would do a search of this site this has been debated before. My advice - a mix of cash, travellers cheques, plastic and an account with Western Union would serve you well with emphasis on the cash in mostly small USD notes.