It doesn't work that way. It is not the price of the download/upload capacity.
If a company in London buys a link to SA, they pay x. If a company is SA buys a link to London, they pay x*5 for 1/2 the capacity.
Similar to the price we pay (used to pay?) for international calls. Everyone knows it is much cheaper to call SA from the UK than calling the UK from SA.
So if your ISP make a london office and then buy from there to here instead?