If you want a good, all around STEM degree that is useful for just about anything, get a degree in mathematics. When I was looking at graduate school a few years ago, just about every program had a list of specific undergraduate degrees that were a prerequisite for admission, and a degree in mathematics was on every single list. If you want to go to business school, medical school, law school, engineering school, get a masters in psychology, biology, international government, aviation management, or just about anything else, an undergraduate degree in mathematics will meet the requirements. If I had to go back an do college again, I would get my degree in mathematics.

Along those lines, I did look into getting a second bachelors in mathematics a few years ago, and Chadron State College in Nebraska (a regionally accredited brick and mortar school that is part of the University of Nebraska system) was offering a distance learning bachelors in mathematics for around $6,000 per year, flat rate, regardless of residency status.