I have a BA in cognitive science and work for a research center at a university. For reasons that feel silly now, I never took more than the required minimum of math and stats in undergrad.
To correct this oversight, I've been taking courses in these subjects in my spare time. I discovered, to my surprise, that I enjoy (undergraduate) math and can do well in it. I started with sophomore-level introductory courses in linear algebra, multivariate calculus, and differential equations, and have, over the course of several semesters, worked my way up to proof-based, upper-division undergrad courses.
I've also been taking classes in applied stats at the university's graduate school of education. They are much less rigorous, but more practical.
Between math, stats, and various odds and ends, I've accumulated 36 credits in post-bac coursework, so far getting straight A's.
The question is, what now? I don't really want to join the applied stats program here.
If I keep taking courses in math, I can finish the undergraduate requirements for the major in another 2-3 semesters. Would I make a credible applicant to a master's program in mathematical stats or applied math?
My original plan was to join a PhD program in one of the cognitive sciences, but I'm rather disgusted by the proportion of researchers in these disciplines whose quantitative preparation is scant or nonexistent. I don't want to waste my BA preparation, but at the same time I am intrigued by my developing interests and abilities. Maybe I can combine the two somehow?
Bonus question: I may sooner or later lose tuition remission benefits. I can't really afford to pay for part-time undergraduate tuition out of pocket. Would I have any way to complete the undergrad math curriculum? (No, community college does not offer fourth-year math.)