If the miserable pay conditions in Early Childhood don't improve chances are you will never have to pay it back anyway.
Our last B. Ed has not needed to pay a contribution previously however she did work less than 30 hours a week.
I guess this will change now with B. Eds requiring to do more hours and if you are already in a full time position as well but at award wage which is around $27.50 an hour.
You can earn just over 49k before starting to pay HECS (HELP repayment thresholds and rates table here). 49k at 27.50 an hours with no other taxables (fringe benefits etc) is just over 34 hours per week.