Hey, I used to live in Perth (and going back there soon), while the cost of living can be high, it is lower than other states (e.g. Sydney), and the wages are typically higher. There is just me and my partner, our rent was $480 for a 3 bedroom house, electricity about $80 per month, internet and foxtel (sky equivalent) was also about $80. Petrol is cheaper than England from what I remember, and cars are also pretty reasonable. A salary of 90k will be more than sufficient to cover you all in my opinion!
Check out gumtree.com.au it has everything you could ever need, we furnished our whole house for under $1000 (and nice stuff too), just be prepared to bargain!
Enjoy Perth, its amazing!