Have a look at the Adoption section here Adoption, Permanent Care & Fostering

The costs for local adoption are not very high, overseas adoption is when you start getting high costs.

In Victoria, check out this Adoption and permanent care - Department of Human Services, Victoria, Australia
Adoption and permanent care - frequently asked questions - Department of Human Services, Victoria, Australia

The first step would be to go to an information session, and see if you think it miht be right for you.

take care