I stayed in a very modest...
I stayed in a very modest hotel in the Quartier Latin. MARIGNAN is the name. There are many other small hotels, I remember scouring the web and I came across several websites with links. You can also take a look at Rick Steves' Europe Guidebooks. I'm not plugging him, but his books are slender and chock full of information.
I was in Paris during early March 2000. It is important to book far ahead for most hotels/motels in Paris, peak season or not. As there are many conventions and shows year-round in Paris, many of the more popular places have been booked months in advance. I'm just telling you what I found out, the hard way. At the time, it was $80 USD/night for a double room (2 separate beds, one of which was larger) with a wash basin/toilet, shower outside of room (however, this was not a problem as I never had to wait for anyone).
Unique Quality: MARIGNAN like many other small hotels offers a minimal breakfast (bread, butter, jam, juice, coffee). In addition, the owners have detailed information on many of the sights worth seeing and activities worth pursuing while in Paris. For me, all I really needed was a clean and centrally located place to sleep, and Marignan fit the bill.
When I was there -- I think the husband provided better service than the wife... but maybe that was me. It seems that now they have a website (something that was not available when I visited) -- so now you can reserve online, etc.