<font face="Verdana, Arial, Helvetica, sans-serif" size="2">Any idea on rail prices from the hotel to downtown?</font>
€7.70 one-way, including connection to any metro within Paris. Trip time is about half an hour.
http://www.adp.fr/webadp/a_cont01_an...E006DB7EE.html
If taking a train late at night, try to take one which doesn't stop at the dodgy northern suburbs between Gare du Nord and CDG.
The CDG Sheraton is nice and quite new, but not particularly affordable.