Sorry about running out of hosts! It's a rough time of year with all the second years in board studying land and the M1's will just be getting back into a routine after break. I think there are also just a ton of you coming, which is great, but they're aren't that many of us!
I would recommend checking out the Mile North Hotel. It's on top of campus and every time I've stayed there it's been about $150 for a suite. So split a few ways, it wouldn't be bad at all! Actually call them and ask about Northwestern discounts/AAA/ whatever. They will work with you. There's also a few hostels around Chicago that I know some people have had good experiences with, but I don't know a ton about that. Lastly, if you stayed with a student host, I wouldn't be afraid to reach out to them and ask if they have room for you. While I'm sure there are people who have something going on that weekend or are really burnt out from hosting interviewees all year, I'm also sure there are people who either completely forgot about the hosting email or just never actually got around to signing up and a few more who would be willing to host if they realized that more hosts were really needed.
Hope to see you all in a few weeks!