To clarify what I said earlier
The two main reasons for the end of Afrikaner National Party rule were
1) The deeply religious National party could not maintain the intellectual rigour to defend a morally repugnant system against the tyranny of numbers with no allies
2) They ran out of money
Having a complete advantage of high tech military equipment made absolutely no difference to the final outcome.
At least pumping billions of dollars into your own country even in the weapons industry generates economic activity which the government can get some return in their treasury to maintain the system.
There would have been nothing gained at all (except debt) by spending the same amount of money on weapons oversees
The arms embargo delayed point 2
I believe you have some good points. Despite everything it stood for, the South African apartheid regime still ran what was probably the best economy in all of Africa for about the same reason Israel does in the Middle East: if it didn't, then there would've been no more country.
But the South African economy is built on a immensely large bedrock of gold mining. When they
did buy weapons from overseas (the Centurions in '52, the Mirages and SS.11 ATGMs from France), they were able to pay with actual money right on the spot.
That's why most governments were willing to do business with the South Africans even though they disliked the regime, much like why countries still buy Middle Eastern oil.
Heck, in the 80s, when the economy was down, the South Africans were even contracting out work to American machine shops. My dad made blasting cap holders for a South African mining company that couldn't find the machining space in South Africa. That shows you just how insulated they were from the economics of the rest of the world, and what the embargo was doing: it was the early 80s, we were in a recession, and the South Africans were contracting out machining jobs they were too busy to do.
So I believe I'm still going to have to disagree with you. In my mind it still comes down to whether it's cheaper to buy a military or build one, and it's always cheaper to buy one. I think we might just have to agree to disagree on this.