While searching for per capita income at Mother Jones, AKA MoJo, I found this that says Puerto Rico is the happiest country surveyed with a per capita income of less than $10,000:

What You Think You Know about Happiness and Why You're Wrong

Commentary: Some number-crunching to accompany Bill McKibben's Reversal of Fortune in the March/April 2007 issue of Mother Jones.

By April Rabkin

February 28, 2007

You might think that richer countries are happier. But there's actually no correlation beyond about $10,000 per capita income. See how each country compares on this scatter chart. One surprise is that Vietnam, with a per capita income of less than $5,000, has been just as happy as France, with a per capita income of about $22,000. The happiest country surveyed was Puerto Rico. The unhappiest were Indonesia, the Ukraine, and Zimbabwe. Within Europe, the happiest countries were Denmark, Ireland, and Iceland.

http://www.motherjones.com/news/featurex/2007/03/happiness_extra.html