It’s great when your work is valued. The only concern is that after your business trip, another client might come up who also needs negotiations, or you’ll have to push your vacation back again. South Africa is quite modern, one of the most developed countries in Africa, so renting a car there is never a problem. You can check what cars are available to rent here: https://getrentacar.com/en-US/south-africa . After that, you can arrange the booking and rental terms directly with the owners, especially since you have negotiating experience.