Mobile data in South Africa is actually pretty cheap in absolute terms, though of course it's still extremely expensive compared to average income.
[1] http://www.vodacom.co.za/vodacom/shopping/data/prepaid-data
USD(Out Of Bundle Rates Per MB) * 1024MB = USD(2) * 1024MB = $164 ~ $150
You would have to really cherry pick the worst case possible scenario to be paying R1 per GB and even then R1024 is $82.44.
Contracts come with data included, all the networks have data bundles, most of them run frequent 2-for-1 style promotion deals and you could always shop around.
Once you factor in all of that, mobile bandwidth is pretty on par with most of the world. Really expensive when you take into account people's incomes, though.
ADSL and other fixed line / point-to-point options are much cheaper once you require anything more than a tiny amount of data, but still really expensive considering the typical South African's income.
Things are very different from the first world, but you have to factor in physics too - we're at the opposite end of the world of just about anything you would want to connect to (latency!), our neighbours didn't all have connections already set up that we could just piggy-back off, etc.
It all got a LOT better in recent years.
These costs trickle down to end users. Even in "progressive" (heh) South Africa 3G can cost as much as ~$150 per GB (so called "out-of-bundle").
I was attempting to set up IMAP in Thunderbird for my parents (who are forced to use 3G due to location) - the obvious merit there is the cloud backup of their emails. To conserve bandwidth they previously had POP3 set up to download headers only. This is impossible to set up with IMAP because, according to Thunderbird HDD space is more expensive than bandwidth and hence re-downloads items if you choose to have headers only. This is a well-known piece of software.
Keep the high costs of poor little Africa in mind when designing your software. Many of us are lucky enough to have access to "high-speed" 10Mbps uncapped copper but there are significant amounts of people who are outright extorted by the cellphone networks.
Please design your software to be kind with bandwidth. Latency isn't the only issue and, in fact, of all the people I know only gamers care about latency (because we have the bigger bandwidth/speed problem to deal with). The average African is quite happy to wait 1s for a website to load, they aren't happy if that page costs them $1 to load.