Most of hotels near APC are more expensive.
Here is the list with
prices and distance to APC. There are options of hotels in the
center of Paris in Quartier Latin, some of which have reasonable
price. Here is the list.
One can reach APC building from Quartier Latin by RER C or
metro. From RER C station 'Saint-Michel Notre-Dame' 2 stops to
'Bibliotheque Francois Mitterrand' takes 5-10 minutes. Take the 'south'
exit ('Grands Moulins') and walk another 5 minutes. APC building is on
the picture below. Some less expansive options are here.