They're all expensive 🙁. I'd look up the subway line and try to pick a hotel that's somewhere near an entrance point. I think I stayed at one that was at the very north most green line station - a small hilton i think. Make sure you arrange it fast though, they asked me to come on sept 28th when it was the 18th already and the cheapest room i could find was $300, second cheapest was $1200 a night. I called ~30 hotels too, most with absolutely no vacancy.
To be honest, I'd recommend staying with one of the students through that offer they have!