Before school care is $10 for us (if you drop off an hour before school or 15 minutes, no difference), but that does include breakfast. After school care is $15, even if it's just for 10 minutes or for 3 hours. They provide afternoon tea. But, as mentioned you get CCB & CCR for those too, so that reduces significantly.
BUT, as your child gets older you can drop them off early/pick them up late without needing before/after school care for short periods of time and they will start having activities before/after school too like music, sport, etc.
If you are able to I'd try & do a school drop off/pick up once a week or so, especially in Prep so you can see your child's room/etc and it will help you feel more connected.
The challenge for you will be to make sure you save that extra money but you're doing the right thing to be thinking about it now. Be strict with yourself and put at least 80% of what you were spending on CC away into savings for a rainy day. I think you'll be looking at $15,000 to $20,000 a year for private school high school fees (in todays money terms). BUT, then you add $500 for uniforms, another $500+ for camps/excursions, maybe another $1000 for a computer and then random other things and it can really add up.