Modest Accomodations in 3e/4e Paris and in Sceaux, France

A friend and I shall be going to Paris on 24 September on very short notice.
A good weekend rate on AA and some interesting concerts at the chateau in
Sceaux are the motivation. We would like to either stay in Paris somewhere
close to metro St. Paul and then commute by RER to Sceaux, or stay in Sceaux
over the weekend. Time is of the essence so I hope someone in this group
will have suggestions on places to stay in the Marais in Paris, or in
Sceaux. We are looking for clean but inexpensive places. Any other
information about early music or early dance performances would also be
appreciated.

Thanks in advance,

Arthur Hornig