funny this is exactly whats happened to me the last few years.
i just took up a full time job and quit school for a while, having part time jobs on the side but taking breaks for a few months at a time. The amount of money I had to pay wasn't near 18 grand but it was still quite a bit, and I am just now to the 500$ mark. I'm hoping to get back into school into spring if I can pay the rest off and raise money for classes.
I think you shouldn't join the military if you don't have to, dude. It's great money sure, not only do you make money and pay debts, but you don't have a living cost. But in the same breath it is really going to change your life and the way you think, for better or for worse.
I took care of my family for a while with rent and groceries and stuff while they paid off debt, and it is hard, but it's something you will probably need to do regardless. My parents debt is still not gone, and it probably won't be before they go, but they've stabilized and I've moved on. I am completely glad I helped out, but I won't deny that I do feel a bit of resentment.
But yeah dude, if you're going to do a 4 year run of school before joining the military, there's no reason you shouldn't be able to find a job in whatever degree you have. If you're not sure about what to go to school for, I suggest just taking a break and getting a full time job. That'll give you time to decide, and you'll be able to pay debt and rent at the same time.