basically it's no problem to get a visa at the NAM border if you've got your onward flight ticket.
Best would be NAM $, but they accept SA Rand as well, which is 1 Rand to 1 NAM $. In most places I found they accept SA Rand, but to get NAM $ with a foreign bank card is a hassle at times. The small ATMs at fuel stations don't accept them, only ATMs at banks take foreign cards.
Enjoy the country!
Only when we pause to wonder
do we go beyond the limits of our little lives.