Another option is.. hop a regional flight to Cape Town (only about $150).. and spend a day or two there...
There is a ton of very cool stuff to do in Cape Town.. a room at the Westin on the waterfront is only about $120 a night.. the hop on-hop off bus that takes you all over the city is only about $25 per day I think.. there are some absolutely incredible restaurants in Cape Town that are very affordable compared to US equivalents..
We rented a car (about $60 a day for a mid sized sedan), and drove down to the Cape of Good Hope... checked out the penguins, seals, bontebok, etc in the area.. that was a super affordable day (cost of a tank of gas and a rental car and a few bucks more for a few meals, etc).. and was an absolutely amazing experience..
The hop-on hop-off tour will take you to the top of table mountain (absolutely incredible views of Cape Town and ocean views of the cape itself), take you to touristy areas on the waterfront, take you to a couple of really nice beach areas, etc.. its easily a full day excursion as well for a very low cost..
Figure $150 for the flight.. $250 for the room.. $120 for a couple of days in a rental car.. $100 for a couple of days of seriously awesome meals.. and another $100 to do some touristy stuff while youre there.. and youre adding in some pretty incredible experiences (much better than I think you'll get in Jo'berg or Pretoria).. and still saving a few bucks over the additional $800 in flight costs for the different days..