Undergrad seeking information about PhD/Masters in Economics math requirements
Before you make any decisions, ask yourself very seriously: What do I want from a PhD/Masters in Economics?

If you want to qualify for a certain type of job, then this will inform your strategy.  If you want to master certain skills, or to explore what interests you, then you may have a different strategy.  If you want an academic job in Economics, then you'll have another strategy, different from the first two.

I suggest you consider three things:

First, you should understand that PhD and Masters in Economics are very different.  Basically, a Masters in Economics will qualify you do to certain types of empirical data analysis.  (I've never heard of a Masters that involves theoretical economics.)

Second, I believe its true that nearly all top or upper-echelon graduate programs in Economics require strong proficiency in mathematics before the will admit you.  This is true even for programs that are no explicitly quantitative (e.g. Austrian).  The math you need is Calculus, Probability and Statistics (based on Calculus), and preferably Ordinary Differential Equations.  You'll need a high GRE math score.  It's very hard to read most Econ papers with out significant math proficiency.

In my opinion, if you really want a PhD in Economics, then you'll bite the bullet and do what it takes to learn this math.  It doesn't require a "gift" or special aptitude. If it doesn't come easy to you, it does require dogged persistence and diligence.

Third, given your interests, I'd strongly suggest that you investigate PhD programs that have a specialty in Experimental Economics.  My University, George Mason, is one of them.  There's very interesting and fruitful work going on in this area, including links to neuroscience and cognitive science, but it requires very strong skills in statistics and behavioral sciences.