According to the travelocity fare listings, you can do CAI-JNB for around 500 bucks, or $1000 if you want Biz on IB. And there are plenty of SEA-CAI fares around the $1000 mark (cheapest BA one is $1276 but SU, TK, AZ, DL and MS all have cheaper options), so there's some saving!
Actually I just checked opodo and it shows SEA-JNB availability on BA (18-30/12) for less than 1000 GBP (incl taxes)!!