I know you can go karting at kyalami, I heard it was 400 for 30min but you get to race those 125 rotax engine karts.
Ive been to compukart in edenvale, wouldnt go back there, old karts that barely work, we could only race 3 at a time, and the whole feel of the place is dirty..
I would try the place out in vereeniging, havent been there yet but planning to go, let us know how it goes.