Like others have mentioned, .co.za is the official South African TLD. You can buy these domains directly from xhttp://co.za, although the process is really low tech compared to Godaddy. The cost is R150 for the first year, and thereafter R50 per year. The exchange rate is currently R6.74 to the USD, but this is volatile and changes daily.
One of the requirements before you register your domain is to set it up in a DNS server somewhere before you buy, otherwise it wont register. This can be quite frustrating and isn’t exactly logical, but its one of the things i have learn’t to live with. To avoid frustration, you may wan’t to pay a bit more and go through a hosting company like Hetzner(a German company with an SA office).