You overlooked one important fact
The Africaners can not afford to buy American farmland.
Those farmers who are "land poor" (own lots of land, but no liquid assets) obviously can't, since they won't be able to sell their land or get any compensation for it from the ANC. Those who have some liquid assets to take with them can still get decent acreage in some western states. It's very unproductive land on a per acre basis, but so is much of the land in South Africa.
For those who accept Putin's invitation, there's always the hope that Putin would protect them from the worst depredations of organized crime and government officials, because having South Africans settle and farm in Russia would be such a great piece of propaganda for his government.