The childcare rebate works according to your combined annual income and is decreased from the maximum allowance as the income goes up. To receive the maximum benefit you can earn a combined amount of about $32000 per year then it is gradually reduced as the income increases.
So an example - my centre charges $53/day in the kindy room - a family on maximum benefit will pay about $6.50/day centrelink pays the difference. A family on around 80% CCB will pay around $22ish. Your best bet is to ring centrelink for a percentage, then ring centres and ask for quotes on this percentage.
If you pass the test for the additional Childcare rebate for the part you pay - ie both parents working/studying, etc. - you will get 50% of the gap (the part you have to pay) back each quarter as a lup sum paid into your account.

Ps your 3 year old kinder is through who? $800 is cheap - the C&K kindy here in Qld charges $600/term so $2400/year!