Hi policy_applicant,
Though I can't give great advice re: funding outside of scholarships, my impression is that there are assistantships and internships that can help pay a few bills. I recently spoke to a professor of mine after class one day about the research she'd be doing over the summer, and I've now got a research assistantship because it happened that she was researching something in which I was interested and felt I was qualified to help. So though I hadn't come to GPPI to seek out that kind of work, I did find it.
Also, it has been my experience that there is an abundance of paid and unpaid internship work. (GPPI is in DC, after all.) The career center can be really helpful in tracking one down, as can professors and other students. There are certainly students who don't work at all during the school year, but many of us think that practical experience is a great way to put what you're learning to use and to expand your experience (and resume) at the same time. Whether your prioritize your internship or your coursework is an individual choice, but I certainly wouldn't say that coursework takes a back seat to internships in general (someone had mentioned that they'd gotten that impression).
GPPI is expensive, but I've always believed that to go into debt for your education is one of the few tolerable kinds of debt. No one can repossess your education. And when you're out there competing against other MPPs in the real word, however distasteful it might be to admit this, Georgetown's name has cache that not all schools do.