Around $4000 is what you would expect west coast to south africa pricing in business class, yes. You can likely find cheaper options from Vancouver, LAX or SFO.

But the emirates 777 plane from seattle is not their best business class seating. Better if you can get a a380 plane which leaves from other cities in US (e.g. from lax and jfk i think, doublecheck before buying).

But anyways, if you're willing and able to pay $4000 for a flight, you can pick any of the options and all should be good. Personally that's too much money just for one roundtrip for me.