The two domain name registration services are www.names.co.za and www.africaregistry.co.za The registration annual cost is of the average of about R110. The registration fees goes to the ISP, and yes there are ISP that provide a free domain name registration service.
Findings from the Forum is that the .co.za is less expensive that .com and that some domain name registration services offer monthly fees other annual and they are in agreement with my findings.