Hi Chelly,
I did the Australia leg (22 days) in October 2012 with pre stop over in Singapore and New Zealand afterwards.
You will find Australia expensive but the costs that are in with JY do help. You will get a evening group dinner on arrival in Perth and a fantastic leaving Meal on a tram around Melbourne, an evening under Ayres rock complete with dinner, A day on the Barrier reef at Cairns which is also inclded in the JY holiday. All the places you will visit do have breakfasts so no problem there!
Yes you will have to find lunches, dinners etc but like I did decided to go with what I liked. Budjeting my meals per day.
Additional excursions can be prebooked (some) and paid for by booking through JY before you go. So no worries there. Any others you like can be paid for to the tour manager or company whilst in that town/city.
Like Cindy says, take as much money as you can afford. I had a Caxton pre-paid card with me for my trip and loaded it with Sterling before I left the UK. I kept a record of my spending, which was easily done throughout the trip.
One tip, Mobile phone calls in Australia are cheap. I bought a sim card for $10 in Perth. Used it every day in each locatio, mainly calling back home and a couple of times for inter-state calls in Australia. Still have around a couple of dollars left on it now. So instead of roming charges here is a good solution.
Anyway hope this helps. Have a fantastic holiday when you go - - I know you will I did!!!!!!
Eric