There is no true "uncapped", the best you will do is a 30Gb cap. The other big question is: Are you downloading local or international? Do you need a low latency connection, ie are you gaming or using it for VoIP?
If it's international low latency and no shaping, you're looking at thousands of Rand and will need to use a SAIX provider.
If you don't need low latency then IS "uncapped" is cheaper, but still expensive R1700 ~ R2700 not sure about shaping (check the IS site)
If it's local you can use one of the IS reseller products, with mixed local/international caps, these would be the cheapest but there's a low international cap and international latency is very high.