To buy a used car here or in SA?

I'm will be doing research for up to a year in both Zambia and South Africa.  I expect to split my time between the two countries.  I need a car to get around.  In South Africa it would make sense to rent, but that is prohibitive in Zambia ($100 a day).  Even though I will be travelling into rural areas I don't think I can afford a 4x4 so I'm looking at a used sedan (saloon).  I am considering buying in SA because I know that cars are more expensive in Zambia and the red tape might be thicker as well in Zambia.  But I am already in Zambia so if it's not too much of a hassle then I would consider buying here.  Either way, I would have to deal with the Zambian bureaucracy.  So specifically, what would be the legal process of buying and registering a car in Zambia, how expensive would this be (including insurance), and how long would it take?  And what is the legal process of driving into Zambia with a car bought and registered in South Africa?  Thank you.