Okay, so you'll be in Zim. Given that, if you think you'll be picking up souvenir-type items on this trip, DO price them out in SA and/or Mozambique, and try and compare the prices to what you see in Zim. In my experience, the prices in Zimbabwe are ALWAYS higher than anyplace else, and you'll want to bring USD to pay for things.
The Roseebank flea market in Joburg is awesome (to me), but you won't be there on a Sunday. In Maputo, the sidewalk to the right of the Polana usually has various hawkers selling the same stuff you'll see all over S. Africa, and it's usually a bit more expensive there (because if you're on that sidewalk, odds are you're staying at the Polana, which makes you rich), but one has to bargain.
If you WON'T be picking up souvenir-type items, ignore this post.
I really need to get back to Mozambique. Thanks for making me totally jealous.