Hi Alan,
As you know I did this tour five years ago so my thoughts might be out of date! I brought 5,000 rand which was the maximum you are meant to take into the country (not sure if this is still the case - no one checked in any case) and I also took some money out of an ATM while there (important - due to the security situation, do not go to an ATM by yourself anywhere in SA). The rand has fallen a lot in value over the last couple of years so you should find things relatively cheap. Obviously credit cards are accepted nearly everywhere. Don't forget to tell your bank when you are going - and if you are getting rand in the UK make sure it is the current issue with Mandela's face on all notes - the previous notes with animals on them are no longer accepted.
Have a great time!
Bob