In Russia, they'd have to contend with extortion by mafia goons and corrupt government officials. That's probably preferable to having their land taken outright and being hacked to death by machetes by marauding Bantu hordes, but the US would still be a better choice for them, at least while we have a sane President (if we had another Obama, I'd say that the South African farmers would be better off rolling the dice and heading to Russia).
You overlooked one important fact
The Africaners can not afford to buy American farmland.