I am traveling to South Africa in a few weeks. Normally before I travel I buy foreign currency through Bank of America and the exchange rate has been similar to CC. However, the exchange rate on the rand is terrible 6.1 to 1. If I simply arrive in SA and pull out of the ATM should I expect what the exchange is now approx 6.8 ( as indicated by hotel deposits already charged) or will it be lower like the 6.1.
I realize there is a small fee pulling it out of the ATM.

So should I buy before or wait??

Any advice?