There are hundreds of thousands if not millions of people who would definitely have more children if they won the lottery tomorrow. Maybe not in your surroundings, or even in your country, but very much so elsewhere.
If this were true (and I don't concede that it is), then you've just stated that the minimum bribe sufficient to persuade someone to become a parent is a lottery jackpot.
Mostly though, people who won lotteries would rather spend that on themselves. Demographic collapse is inevitable, and you'll die without even understanding why it happened.
As the other person pointed out, a lottery jackpot is also far above the minimum, it was just the most obvious example of a sudden windfall. And even then I was considering lottery jackpots here which are usually $0.5m-5m, not tens or hundreds of millions which seems common in the US (I could be wrong on that).
Well, the reason why you choose the absurdly improbable example, is because it's still the least absurd/improbable. Why does this need to be explained to you?