Hi Theresa,
Have you considered starting off as Part Time study?
That way your costs are generally half of what Full Time would be...
I started PT this year, and had Aidyn in 2 days of childcare per week (works out to $50/week after you take the CCB out based on my DP's income)
I applied for through HECS to pay for my subjects, so havent had to pay a cent for that yet.
I also bought all of my textbooks 2nd hand (there is a textbook exchange website where students sell their 2nd hand textbooks, I can give you the URL if you ever think you will need it in the future!)
The textbooks CAN be really expensive though... I am doing 3 subjects next semester and my textbook list is well over $500! And unfortunately I am having trouble finding them all 2nd hand too.
Might have to utilise photocopying or the library for some of them I think.

Queenie - WOW at doing your PhD! That would be so hard... good on you for keeping at it!!