I don't send my boys yet, but I did recently look into it with center link.
The rebate works like the medicare system. Daycare's have a scheduled rate of $2.80 per child per hour. the rebate covers what ever % you are entiled to and then you pay the gap. So the daycare may actually charge say $6 per child per hour. Family daycare is ALOT cheaper as they tend to charge closer to the scheduled amount.

There is also a thing called the JETS rebate. This is organised through centerlink. People who are studying or recieving a centrelink payment are elidgable (sp?) to apply for the JETS rebate. This covers the gap that you would normally pay. You do need to pay something to contribute to the cost but apparently its like $2.

Once you know what % you are entitiled to get through the childcare rebate thing, you just ring around and tell the daycare and they will be able to tell you what you will be paying (the difference).

From what I know without any rebate the general cost of childcare at centers seems to be anywere from $40 to $60 a day per child. If your child is only going half a day you still have to pay the full day rate as they loose a spot for another child once your child is there, regardless of how long they stay. also you still have to pay if your child is sick and doesn't go.