Are you trying to say you are an international student? If you are, you have to pay upfront and there is no hecs. If you are a citizen/PR, you can't get into a full-fee paying place (since 2009). You pay off your hecs debt for both degrees when you start working
USYD provides transfer flexibility, you can transfer even in 2nd/3rd year. With UNSW I think you can only transfer only after 1st year. It's not strange but it will be difficult and stressful in making new friends again. Just stick with UNSW.
This year, it would cost $12,680 with winter school and the upfront discount bonus. It's ridiculous how much winter school costs! The cost of one subject done in winter school equates to the cost of 4 subjects done during the normal semester
USyd says it would look at the best of your WAM or WAM+ATAR. My best mate at UNSW had a WAM of 84 in first year and 86 in second year. He applied for USYD law for two years and he couldn't get in.