I had a similar issue in my IP in bayside area.
I had quotes from a few companies, and if you read the fine print to maintain their warranty was impossible in Qld, ie they said humidity cannot go above 80% or something which is not possible in a QLD summer. Plus the cost was very high.
In the end I got the local handyman/painter for the RE to clean the mould + apply a sealant (so mould wont have anywhere to grow again) + repaint for the same cost as a mould removal company would have charged just to treat and remove the mould. And now the ceiling is all nice and fresh painted.
Plus the handyman gave a 3yr warranty that mould wont grow back.
Ben