(All the mentioned accounts are shaped)
Openweb's 10GB SAIX for R459 per month is probably the best option.
You'd sign up for two of these accounts (R918 per month). Having two accounts of course has it pros and it cons. I can't think of very many but here's a few that immediately come to mind:
Pros
* You get 4*2=8 theoretical concurrent connections if you need to make multiple connections
* You end up paying R45.90 per GB for SAIX bandwidth, which is the cheapest I know of that has no setup fee
Cons
* If you are only going to use one connection at any given time, when the one account gets capped you'll have to change the login details in your router to the other account (not a big con but it's still there!)
If you would like one 20GB account as opposed to 2 x 10GB accounts then I'd say try
WebAfrica (R1140 pm) or Axxess (R1199 pm) but you'll see that getting 2 x 10GB accounts is cheaper in most cases: WebAfrica (R980) Axxess (R1198)
These are the best value for money deals I know of, IE I've only mentioned ISP's that I've had good experiences with and that have good prices
