Cost to travel to Australia from Canada?

Hello! I am a Canadian students that loves to travel. I traveled all over Western Europe (to Scotland, France, Spain, Italy, Switzerland, Germany, the Netherlands and more) for 1 month on a budget of 4,000 Canadian dollars. This included airfare from Toronto to Scotland, food, hostels, entertainment, train tickets, EVERYTHING..keep in mind I did a lot of couch-surfing so I saved a lot of money. My next dream destination is Australia. Can anyone give me an estimate of how much it would cost to travel to and around Australia for 1 month? I really don't have much money, so couch-surfing and hostel stays are definitely OK with me. I would like to do a lot of fun activities like scuba diving around Great Barrier Reef and learning to surf as well.