Hello!
It would be cheaper to buy in South Africa because the value for one USD in ZAR is 8.46. The value for one USD in EUR is 0.76. Therefore, the US dollar is more strong because the value is larger in ZAR, and you would have more money to buy more things.
But anyways, for MORE information, you should know that theoretically there's no reason to believe it would be more expensive in either place. It would likely have to do with transportation costs to the countries in question from where the supplies are made. Because you see, there's no reason to believe one US dollar has greater buying power in either place, so whether you're in Europe with Euros or South Africa with rands, you convert your dollars into the local currency and it will probably cost you the same number of DOLLARS either way. If the rand goes down in value, the prices in South Africa of everything measured in rands would go up, but would they go up when measured in US dollars?
Sorry For the Late Response XD! Hope this All Helps AT LEAST!
Have A Wonderful Day! :)