A FlyerTalk Posting Legend
Join Date: Sep 2009
Location: Minneapolis: DL DM charter 2.3MM
Programs: A3*Gold, SPG Plat, HyattDiamond, MarriottPP, LHW exAccess, ICI, Raffles Amb, NW PE MM, TWA Gold MM
Posts: 100,396
Major Boston hotels practice yield management. They're fairly cheap when there are lots of empty rooms and expensive during periods of high demand, including big conventions and major events.
Don't forget to also check across the river in Cambridge, but be careful that you're close to a subway station.
I wouldn't consider sleeping overnight in a car.