Room rates in a big city will kill you, that's for sure.
For me, flying in from out of town, staying at the Hyatt makes sense. I don't want to rent a car so any savings I could find on an off-site hotel would be eaten up by cab fare. This way I can also stumble to my room if need be and sleep until the last possible second before that first AM session
If you don't mind staying off-site, do a search on the "cheap hotel rates" websites using the Hyatt's address, 101 Harborside Drive Boston 02128, as a starting point. I poked around a bit; the best rates, in this order were on HotWire (though this is the most restrictive in choice), Orbitz and Travelocity.
For people flying in, Travelocity has some great low fares.