Why do you go straight from "10-20 thousand" to "billion," OP?
I'd guess the number is probably in the millions, though I guess it could be around a billion. Definitely not in the 10-20 thousands - even the US's richest 4 percent alone (going by 2010 numbers because it's what I've got on-hand and I'm too lazy for anything but the math) is around 13 million people. That's people making upwards of 200k per year, who are mostly bourgeoisie and wealthy landlords. If we use that income group to represent the bourgeoisie (which isn't entirely accurate, since a small minority of those people are wealthy authors, actors, etc. who may not have other business ventures), and all 195-or-so countries in the world had as many resident bourgeoisie as the US, then there would be around 2.5 billion borgs on Earth. That's obviously way higher than the actual number, though, since most countries on Earth have fewer people and fewer super-rich people than the US. The actual number of people who are that wealthy is absolutely in the millions, but probably falls short of a billion. >>473112
And this probably beats my methodology here by trillions.