In the late 80's, a scheme was introduced whereby degrees were assigned to a number of bands based on your likely income as a result of that degree. At the time, IIRC, medicine and law were in the top band, while eg. philosophy was in the lowest band. Each band had an annual price for enrollment, but they were iirc, $2500, $3500, and $4500 in maybe 1988 or 1989.
You paid nothing during your studies, but once your taxable income exceeded a threshold, you paid an additional couple of percent on your income tax until the accumulated debt from your education was repaid. This was part of the income tax withheld for most salary earners, and so was largely invisible.
In addition to that, students enrolled in a recognized educational institution get an allowance for living costs. In the 80's and 90's, this was sufficient to live on (food, rent) and you could earn enough extra income to get a social life and textbooks and so on without losing your allowance.
Healthcare is basically gratis in Australia too, so it was quite feasible to attend university with a small amount of part-time work with limited or even no financial support from your family.
Over the last 30 years, the repayment percentage has increased, the starting threshold has gone down, the annual fees have gone up, and the weekly allowance hasn't kept pace with the cost of living. But ...
Even without going to the "extreme" of genuinely gratis tuition, there's plenty of precedent for a system which gives everyone a decent opportunity for education regardless of their financial circumstances.