Actually $140k the banks will lend 80% of that so about $110k of that you can use. LMI is 20%.
My calcs you could do no more than about $500k. $100k deposit, stamp duty will be around $15-20k. Even if you went 17 or 18% you can put the LMI onto the loan (it will prob only be $2-3k anyway)...
You have $140k in equity - You could buy a $5-600k house. the more you pay, generally the rental returns are less.
Buy a house in the Gold Coast, the market is warm atm. There are too many units in the GC, I would buy a house