Other points about the Australian system:

• The cost of the university course is subsidised by the government. The government pays the majority of the cost, usually around 70-80%. For example, a Bachelor of Computer Science degree at the university I went to (Swinburne) is currently AU$9k/year (~US$5.8k) subsidised vs AU$39k/year (~US$25.4k) full price.
• The loans for the amount you have to pay are through the government and are interest free. They're indexed for inflation once per year, but this is a much lower increase compared to interest from a bank loan.
• You only have to pay it off once you earn over $51k/year, like you said. Repayments start at 1% of income and are paid as part of your income tax return.
• They used to have a program where if you paid $500 or more of the loan upfront, you'd get a 10% discount (so e.g. if you paid $500, it'd reduce your loan balance by $550).

Note that this system only applies to citizens and permanent residents. International students still have to pay the full price. Having said that, Australian universities frequently advertise at college fairs in the USA, as even at the full price plus flights plus accomodation, studying in Australia can still end up cheaper than the USA, and Americans love Australia 🙂