Would we save money on tax if we buy an investment property?

[tired lady]

I don't really understand how it works but my husband is paying $30,000 tax per year on a salary of $84500 (A LOT of tax!) We live in the desert for his job and only pay $70 a week subsidised rent, we are going to be here for another year and a half at least and his pay will increase. We are kind of wanting to buy a house but cannot decide whether to buy an investment property for around $300,000 or a house for us to live in for about $400,000, the rent we could get for the cheaper house is $300 a week and for the more expensive house $400 per week (the more expensive house will need to be built first). What I want to know is if we would get tax deductions for buying an investment property and if so how much is it and what IS a tax deduction? Like would we get a large tax return or something?
$300,000 is as cheap as they get unfortunately. We live in Western Australia