Most of the hotels in the French Quarter (La vieux carre) are quite expensive. I have found a spot that is actually less expensive than hotels located in the Central Business District. The St. Peter House Hotel is right near Bourbon Street in the Quarter and has rates around $50/night! During big events, such as Mardi Gras, they do raise the rates accordingly, but still you will pay a lot less than at other hotels.
Click the above link to learn more about this great find!