I don't know this area (Montmartre and behind) very well. This is not a very expensive area. There are some "minorities restaurants" which are inexpensive: Morocco, Algerian ...
You may make a search on
http://www.viamichelin.com/viamichel...aurantHomePage
The Entrecote/Relais Venice, which is mentioned in FT Dining is not expensive, but on the other side of Paris.
Inexpensive (but touristy) restaurants are also in Quartier Latin.
Have fun!