Hi antoinetteludick,
Most private schools/model c schools are expensive with some going all the way up to R70 grand a year and some even in the R90s. So if you choose those ones then you have to have reconciled yourself with paying those monies.
But then there are very good government schools as well where you will just pay the normal fees(especially in the suburban areas). There are also semi-private schools which are subsidized by government so they give you private school education for an affordable fee.
Just do your research coz most of these schools have website and their info with fees breakdown will be there.
The 'education' itself is pretty much the same if you ask me, the difference is in the teaching(some private schools here in joburg kids don't even use textbooks anymore they use tablets for example) and other extra curricula activities like sports and all that.
I hope this helps