I don't really consider having money in order to be happy. At least that was always my thinking before I had no money.
Right now I have no cash and am eating into my £200 overdraft at my bank, and that's just buying food and the occasional 'luxury' like a bag of chips (fries?). But when I get regular work at the place I'm cleaning at the moment, I'll have basically enough to live on. I'll work 2.5 hours a night and make about £90 a week, so... £360 a month... which is... £4320 a year I think. That will pay my rent and food and I can live comfortably on that.
But I guess if I really wanted to splash out I would need at least double that, because I'd want to buy a swimming pool and DVDs and latest tech like iPods and whatever. But I consider myself happy now and I'm in the negative on my bank account. So I guess it depends.
Maybe what I'm saying is my happiness levels don't correlate with the amount of stuff I have.