Not sure exactly what you are asking, but it seems you want to stay at the airport for cheaper hotel rates and commute into Paris to visit the sites.
http://www.ratp.info/orienter/f_plan...eroport&fm=gif
I wouldn't do that as you will eat up all day sitting on trains. So the tradeoff is more in transport cost and time - lower hotel rate. Ultimately you must make the choice. btw, head over to the Paris forum for lots of good info on getting around Paris.