Practical accomodations in Paris : From Denfert Rochereau RER-Metro station, it takes 35 mn by RER B to get in Orsay-Ville.
Visit the following link : Hotels near Denfert Rochereau
Other hotels can be found under the link other options, but be aware Paris is an expensive city. However, you can get interesting deals if you book in advance.
In Place Denfert Rochereau
Hotel du Lyon, Hotel Floridor, Hotel du Midi, Villa Montparnasse, Hotel Sophie Germain de Paris
Mariott Rive gauche is close to the RER B station of Denfert-Rochereau and offers nice rates if you book early
Quartier Latin close to Port-Royal, Luxembourg or Saint Michel stations : 40-45 mn to get to Orsay-Ville, easy access too
Paris 5eme arrondissement, quartier Latin area
Warning : If you decide to stay in Paris, check the size of the room and its location. Sometimes single rooms are just impossibly small to live in! Court-yard locations are the best in order to avoid noise from busy streets.
Hotels near Orsay:
Hotel Le Village in Gif sur Yvettes (towards the country side). It takes about 20 mn to get to Orsay-Ville (5 mn with RER B + 15 min walk from the hotel to Gif sur Yvettes station).