Well unlimited 192 kbps ADSL is R1230 and you can download about 60GB per month with it. Unlimited 512 kbps ADSL is R1500 per month and you can download 160GB per month with it ...
so cost is as follow:
ADSL 192 kbps = R1230 / 60GB = R20.50 per GB (R850 installation and modem)
ADSL 512 kbps = R1500 / 160GB = R9.40 per GB (R850 installation and modem)
ADSL 192 kbps with 30GB cap = R930 / 30GB = R31 per GB (R850 installation and modem)
iBurst 9GB = R1100 / 9GB = R122 per GB (R2914 activation and modem)
iBurst 1GB = R470 / 1GB = R470 per GB (R2914 activation and modem)
MTN GPRS = R500 / 1GB = R500 per GB (R0 activation and modem, assuming you have a cell phone that supports it, if you don't, one will cost I guess R500 or so)
so who want iBurst? If you don't need much get GPRS, well you already have it on your cell phone. You don't have to invest thousands of rands for useless modem. there is no activation fee etc. If you need a lot, get ADSL, it is only couple of times cheaper and far more reliable!