Metal detectors

I’ve always wanted to get a metal detector so I can go fossicking for gold in the outback somewhere. Then I found out that metal detectors come in all size and price range and I’m already confused as to which one I should be getting. I think a rule of thumb is that the dearer the price the better the detector. But then the expensive ones can be as much as a few thousands dollars which I can never afford. I could go for the cheaper ones but then are they any good?