We will be going to the Loire Valley after arriving at CDG. It appears that we may need to take RER and metro to transfer and may need to stay overnight in Paris (so sad, huh). I am looking for affordable options in the Austerlitz or Montparnasse gare areas. Any suggestions
Here are some Montparnasse area listings from my 2004 Lonely Planet Paris guidebook. Prices probably are out of date.
Hotel de Paris, 51 av du Maine. Metro: Montparnasse Bienvenue. d €75-90.
Hotel Delambre. www.hoteldelambre.com.
Hotel Odessa Montparnasse. www.paris-hotel-odessa.com.
Celtic Hotel, 15 rue d'Odessa. Metro: Edgar Quinet. d with shower & toilet €57-63.
Hotel de Blois, 5 rue des Plantes. Metro: Mouton Duvernet. d with shower €45. d with shower & toilet €49.
I would not recommend the area itself around Austerlitz - it is one of my least favorite in Paris.
Montparnasse swarms with hotels and there are many options to look for. The area is lively with lots of history near by.
As for hotel - there is a nice small hotel (boutique) Hotel Danemark.
I have stayed here many times in the past prior to moving here. It is a small quaint hotel just off of boulevard Raspail - close to le jardin du Luxembourg - and walking distance to boulevard Montparnasse.