I'm beginning my second year in the DO-PhD program at MSU. Chances of getting in depend strongly on the evaluation of candidates by the program director, and the feeling I have gotten is that they will only encourage that you apply to the PhD if they truly think you are cut out for it.
Dr. Justin McCormick is the program director at the moment and he has the final say. I would say he looks for a strong GPA, a good MCAT score, strong research experience, enthusiasm for the program, and personality. However, I do get the impression that they will give you a chance if you are exceptional but have a lower MCAT or GPA.
The process works as follows:
1 - indicate your interest on the secondary application from MSU and fill out the essays
2 - wait for the medical school to invite you to an interview
3 - wait for the DO-PhD program to invite you to interview as well - for out of state applicants this is generally on the same day as your medical school interview
4 - do those interviews - Dr. McCormick will generally give you a good idea of whether or not he wants you to apply to the PhD
5 - get accepted into the med school
6 - apply to the PhD program, and come back to interview at recruitment
7 - wait for PhD to let you know if you're in
8 - celebrate that you're stuck in one place for at least the next 6 years, but more likely 8
MSUCOM costs an average of $10,000 a year, and provides a stipend of $28,000. I'm pretty happy with my decision, but it's not for everyone. The program is long and difficult, and will definitely test you. Feel free to message me if you want more info.