A lot of other South Africans here. Bly om te sien ek is nie alleen nie ^_^
What area are you in? Gauteng? Cape Town? Are you planning on using local dealers? The only real major PC company is Chaos computers, which kind of sucks. Many games retailers though - SA actually gets PC games for cheap compared to other countries.
To put it honestly, you're looking at a GTX 550 ti at best. 6850's are selling for R1999 and 6870's are going for R2499.
You could however, order online and get it somewhat cheaper from overseas. I'm personally trying it out and it still works out rather expensive but I save about R400 on a 6950.
Everything in SA is expensive, which really sucks since we make 3rd world income.
Even cards like the 6870's will take some strain with games, it won't handle Metro 2033 @ max 1080p resolution.
If possible, save for another month and buy one of the new Radeon 7 series cards. Look into the Radeon 7770 or 7790. That might just be perfect for your needs.