Cheaper option is Sea freight but that depends on ship sailing time and arrival time (And Pirates

)
You can plan your trip to arrive in SA same time as the ship docks
If you prefer Air Freight,(This is the expensive option), make sure the packing box is small as possible by removing front wheel (To drop height) and Handle bar to reduce the width. After a certain Kg in weights, Airlines charges by Volume, therefore the smaller the box the cheaper the price.
I have shipped a bike out to Africa almost 3/4 yrs ago and did the above(Total Cost was under 1k)
To cut Cost,I used a local packer who did a great job for me and delivered the bike to the airport for me too.
Shop around as much as you can, Try and work out a box diemsions and approx weight. ask Airlines to quote you on that .. I used Davies Turner they were very competitive in price.. Good Luck..