Psychologist and Nobel Laureate Daniel Kahneman says millions of dollars won't buy you happiness, but a job that pays $60,000 a year might help. Happiness levels increase up to the $60K mark, but "above that it's a flat line," he said.
$60,000 is about the midpoint of the income scale for American families - 50% makes less than that, 50% make more. This is a reachable income standard for nearly all two-income couples, and for the great majority of college graduates by themselves (and much more with a second income in the family).
Once your basic survival needs are met, even in an expensive country, happiness mostly depends on who you spend time with and how well you interact.