http://www.trivago.com/ compares prices of the same hotel from different websites so you don't have to spend hours searching for the best price! What a great time (and money) saver! ... I am not affiliated with this website or it's company or whatever in any way. Lol
Affordable Paris: 17 Hotels. This article by Travel & Leisure is a decade old, but the hotels are still reasonably priced by comparison. We've stayed at Hôtel Le Ste.-Beuve in Montparnasse once before.