Research your area. Off the beaten track offers much better value than areas like cape town which have become expensive tourist traps. Check out areas along the garden route and west coast.
Try and use local estate agents. They will have a much better handle on the areas and prices. I have listed some of the well known ones below.
Pam Golding Seef Aida
You will also need to change your pounds into south african rands for the purchase. This company is really good. http://www.foreign-currency-uk.com/