Scoop,
I live in Boston, and I've been trying to find reasonable rates for some friends of mine coming up in October. Good luck. Rates I've found range from $200-400 per night. Oh, well. :-(
If you don't need to stay in the city, though, you may have better luck. Try checking into hotels in suburbs north of Boston and convenient to the MBTA Commuter Rail. These trains are not that expensive and will take you right into North Station, which for a Bruins game, is conveniently located INSIDE the Fleet Center.
You can check the MBTA Commuter Rail map and schedule for the names of stops to use whilst enquiring for hotels. Goto
http://www.mbta.com for more information.
Best of luck to you!! GO BRUINS!! 8-P