Beijing has plenty of hotels ranging from expensive big western chains to smoke-filled, poorly lit hovels. On one extreme it’s almost obscene watching rich Americans walk around the Holiday Inn at Lido where the rooms run $200 per night and hookers fill up the bar next to the lobby. We’ve stayed in hotels on the dodgier end of things with daily 7 am construction and which have had elevators crash to the ground.
Accommodation is not as cheap as it should be considering how much everything else costs, but a dorm bed in a hostel can usually be had for 60 RMB.
For longer term stays, rents can start as little as 500 RMB/month for a shared room a 30 to 40 minutes subway ride north of line 2. A more typical rent might be 2000 RMB/month for your own bedroom is a convenient neighborhood (but not Chaoyang.) There are also more expensive, gated western communities on the outskirts of Beijing but no Road Junky would actually pay to stay in one of these.
The Olympics in August 2008 have elevated room rates and many Chinese and ex-pats are offering to sublease their flats. Find Beijing is offering good deals on places to stay during this time period.