Definately CSP, as other people have said, if you get the UAI for the course. You can finalise your preferences after you get your UAI.
For example, my course under DFEE would cost ~$18k a year, so times that by 4, and the cost is quite large. Under HECS-HELP (CSP), the cost would be about ~$8k a year for 4 years (plus yearly increases) and paying that upfront would get you a 20% discount. I hope that example helps.
Actual HECS-HELP fees are determined on a per subject basis rather than the degree you do. Most subjects fall into Band 2, but some subjects like teaching are cheaper in Band 1 and law is more expensive in Band 3. So, in other words, you could be paying more or less depending on which subjects you do each semester and also how many you do.