not sure if you know this. All uni students pay the government fees to study at uni. It's called the HELP scheme. Australian citizens and those on a humanitarian visa are able to defer paying it until they have finished studying and are earning over a certain amount. It then gets paid back as a percentage of what they earn through the tax system. Those on residency visas must pay it up front each year. These fees are between $4000 - 9000 a year depending on what is studied with courses like law and medicine the most expensive.
We are in this boat next year as daughter no. 1 is our only child not to have dual ciizenship, having been born in Uk when we were back there. As she has lived here for 16 out of her 17 yrs she may as well become a citizen, but for newies there is a waiting period for citizenship. You won't lose UK citizenship by becoming an Aust citizen aswell.