How Much Is Enough?

I met some friends for lunch today and the topic of "how much is enough came up". My friends, a nice young couple about my age, were telling us that for them to live comfortably in Singapore, they would need a monthly income of about $7500. That amount includes car, house, daily expenses and gym membership. The question was thrown to Adrian and I. Honestly, I have not made any serious calculations. But I reckon it should be around that amount. That set me thinking. We have no kids and our monthly expenses were already as such when we were in Singapore. What happens when we have (readers, don't let your imagination runs wild)? How much is enough then? Some of my friends may argue that when children arrive, you basically change some of your spending patterns e.g overseas trips to insurance, entertainment expenses to paediatric spending etc, such that your monthly requirements are kept to about the same as before.

Pondering further, I think the crux of the issue lies in what kind of standard of living are we after? There are families who can survive happily and decently with half of our monthly income. 所为知足尝乐嘛 :) 你的幸福款项是多少呢?