If you are staying a full week, renting an apartment as a group may be a better option. Appartments in the 5th, 6th, or 13th arrondissement (district) will be reasonably close to the workshop. Loctions near metro lines 7 or 10 will be most convenient for LPNHE; those near metro line 14 or RER C will be most convenient for APC. Search google for "paris vacation rentals" to find sites like this: