Hi, I know I am coming late, but just to add to this discussion...

MBA is a terminal professional degree, not an academic degree like the PhD. Social science research methodology will be different than what they teach in a professional degree program, unless your program requires social science stats.

My advice is to finish the MBA with flying colors and then use those credentials to apply to a PhD program in economics. Realistically, PhD candidacies are going to be filled by students who have been in the discipline since undergrad and who have done original research via their undergraduate and graduate thesis.

However, if you design an area of research for your dissertation, you can very easily in an economics program make it cross disciplinary with psychology. It requires have a broader base of published literature, but still...something along the lines of the psychology of consumer spending....the psychological effect of triggering advertisements. These are just examples and maybe they have been written about ad nauseum. I don't know...psych is not my area.

But then you could easily get a job teaching in a psych department with the right job offer and course design, even with a PhD in a different social science. If you wanted to do clinical work, then there are professional degree programs that are two and three years long dedicated to clinical practice.

Realistically though, without a strong psych academic background, it will be hard to apply to an academic psych program. I believe the PsyD is also a research/academic degree even though it is much more geared to the clinical setting than a PhD.

Just a thought though...