I wa running this through on a different trip, and a couple other things for consideration are:
- would you prefer 2 business class trips to SA or 3 in coach? For me I'd pick business but for you if you are on a really tight budget I could see the appeal of coach.
- are you hard up for miles? Paying cash on a cheap flight (as long as it isn't a half miles ultra-discount fare) could yield 16k miles (I think united?)
- how do you sleep in coach? If you have an empty plane you could get a row to yourself