How much will 1 month in australia cost?

i'm going australia 1 month,
thinking of firstly flying adeliade , spending 2 , half weeks there , want spend time @ beach wanna loads of fun stuff
flying cairns spend few days there , want experience great barrier reef possibly boat trip , snorkelling,
fly sydney , spend week there , want go bondi, opera house, harbour bridge, want experience can while there , how think flights be? have accomadation in adeliade , sydney not cairns, ant ideas of places stay , how cost? , costs of spends , going of these places , entry, food, travel etc, much

i'm going australia 1 month, thinking of firstly flying adeliade , spending 2 , half weeks there , want spend time @ beach wanna loads of fun stuff flying cairns spend few days there , want experience great barrier reef...

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