If you're not interested in public health, and it doesn't sound like you particularly are, then I don't think it's a great idea regardless of the cost. Maybe it's just because emotion doesn't come through well these kinds of posts, but I'm not hearing much enthusiasm from you about the specific issues related to public health. You mentioned that it's a "free degree" at your school, but that's not a very good reason to spend a year of your life doing it. It'd be much better to find something you're really passionate about and pursue it. Maybe that's lab research...apply for a Hughes Fellowship or spend a year at the NIH, or do clinical cardiology research, get an MBA, or do whatever else it is that REALLY sparks your interest. An MPH is a long and difficult road if you're not all that interested in the subject matter.
What other degrees/programs are offered at your school? I'd think long and hard about other opportunities that might stimulate you a bit more.