Ah sorry... I was just being sloppy, what I wrote doesn't make sense. What I meant was "order of magnitude", but I'm not sure how to write that; Big Theta says two functions grow within a constant factor of each other, which is vaguely similar to the notion of order of magnitude. Maybe it should have been "$~10^9$" or just "$10^9$".

(By the way, my reasoning was 10^4 for current cryonics prices, times 10^7 or 10^8 people, times 10^-2 or 10^-3 assuming a fee of 1% to 0.1%.)