I would definitely recommend South Africa. You can fly into Cape Town, flights are around £500 I think. I booked through Trailfinders.
It isn't really Scuba diving, as you stand in the cage wearing a mask and snorkel, then just duck down when the sharks come lured by bait on a line. I asked why they didn't offer diving with a tank so you could just stay down there and look around but they said that the bubbles tended to scare off the sharks. Not quite sure I believed that, but there are so many boats out doing the same thing that any little thing that might deter the Sharks from coming to your boat isn't great.
There are so many things that you can do out in South Africa, that I would recommend you only spend a couple of days seeing the sharks. Cape Town is beautiful, there are lots of great places to see on the Garden Route, and the diving on the East coast near Durban is fantastic.
Is there anything else more specific that you want to know?
Lee