I am a little bit in a hurry, so I don't have the time to give you many details right now but I'll come back to you later:
As you are coming from CDG and going back there again, then want to go to Versailles, in order to reduce your expenses, buy a carte visite for all the zones and for the lenght of your stay directly at the airport. This way, you won't have to spend any additional money on transportation during the whole stay and use all the metros and buses.
Two good restaurants at reasonable rates:
http://www.domainedelintillac-paris.com/La%20carte.htm
http://mmmm.free.fr/scripts/script_d...sto.php?id=301
both have good deal menus at lunch and evening