I was thinking about this topic earlier today, and i realized that the largest black ethnic groups on earth could totally afford to do this. We living badly out here but there are many more people living worse than us, who would gladly sell land in exchange for food and a chevy pickup truck . Coincidentally, the largest black ethnic groups are all fighting among their people for land, (ados/fba, igbo, yoruba, hausa, oromo, kikuyu, etc).
It would be something modeled after the Louisiana Purchase, but for full sovereignty not land leases. Wouldnt even need a whole country; just a decent piece of land for a citystate. Even more so than money, i think the UN power balance would be a bigger issue; so you might have to buy 3 countries simultaneously to appease the western faction, russia faction, and china faction of existing global bodies.
Look at you nikkas with your warped colonial minds
Its not colonialism if the inhabitants willingly sell you their sht. I think of it as a service.