His A level results can be converted to a university entrance score - best to contact the university he wants to go to and ask them for an equivalence for the course he wants to embark upon.
I would imagine that the visa you come here on will determine whether he pays international student fees or local fees. Aussie universities are not free - the course fees depend on the course - arts courses are cheaper than medicine or law for example.
Here is a link to the fee structure for various student groups at ANU to give you a bit of a clue what you will be up for.
ANU - Student Administration Services - SAS