There 2/3 areas with a RER-B station:

====== Denfert-Rochereau ======

===== Sofitel Paris Forum Rive Gauche =====
7, Boulevard Saint Jacques
75014 PARIS
Tel :(+33)1/40787980
Fax :(+33)1/45884393
E-mail : h1297@accor-hotels.com
Price of rooms* : 165 EUR >> 650 EUR

===== Mercure Paris Montparnasse =====
20, rue de la Gaite
75014 PARIS
Tel : (+33)1/43352828
Fax : (+33)1/43357800
E-mail : H0905@accor-hotels.com
Price of rooms* : 115 EUR >> 234 EUR

===== Mercure Raspail =====
207, boulevard Raspail
75014 PARIS
Tel : (+33)1/43206294
Fax : (+33)1/43273969
E-mail : H0351@accor-hotels.com
Price of rooms* : 100 EUR >> 175 EUR
Remark: need 1 stop on ligne 4

===== Ibis Paris Maine Montparnasse =====
160, rue du Chateau
75014 PARIS
Tel : (+33)1/43220009
Fax : (+33)1/43202178
Price of rooms* : 79 EUR
Remark: need 3 stop on ligne 4

====== Saint Michel ======

===== Mercure Paris La Sorbonne =====
14 rue de la Sorbonne
75005 PARIS
Tel : (+33)1/56243434
Fax : (+33)1/56241960
E-mail : H2897@accor-hotels.com
Price of rooms* : 120 EUR >> 225 EUR
Remark: need to walk

====== Chatelet / Les Halles ======

===== Novotel Paris Les Halles =====
8 Place Marguerite de Navarre
75001 PARIS
Tel : (+33)1/42213131
Fax : (+33)1/40260579
E-mail : H0785@accor-hotels.com
Price of rooms* : 186 EUR >> 418 EUR