Between rent, student loan payments, health insurance, bills, and car loans, and food, I think we maybe have $500 left to throw around each month. If we were paying against a mortgage, that would basically be zero.
The most financially effective way to be a programmer is to work remotely for someone who pays SF or NYC salaries and live in a moderate COL area.
I've always seen the rental income requirement you stated phrased as "monthly income must be at least 3x monthly rent", in case the 40x thing threw anyone else off (40/12=3.33).
I've recently seen 45x monthly in Manhattan and LIC (Queens).
And, as a sibling comment stated, it depends on location. I think $80k is right for most areas of the country. If you live in NYC, SF, LA, or another place with really high cost of living, adjust accordingly (which is probably like 2.3x).
You may not be able to afford a house in the area you want, but you can certainly afford a home. Here's one with a mortgage for $89/mo.
http://www.zillow.com/homedetails/207-1st-Ave-W-Gackle-ND-58...
Two people can easily live on $40-50k in most areas. Eliminate all the unnecessary expenses like $150+/m in phone payments, $50+/m for cable, etc.
for the $80k number.
In case you haven't seen it, there's another paper that argues the opposite: more money does make you happier (but only if you know how to use it). http://scholar.harvard.edu/files/danielgilbert/files/if-mone...
I make more than $80k and I can certainly say that I was less stressed before I took a huge pay cut. On the other hand, I like my job more so I guess I might actually still be happier. All else being equal though, if I made more I imagine I would be much less stressed..
The advantage of big money isn't just charities and companies - it's having your time back, since you're not tied to getting an income from it.