Although I always stay with friends while in Paris, I sometimes rent an apartment so that I can stay out later and/or get up later for my airport departure. Renting is also a perfect solution for my friends visiting from Belgium; the train from Brussels only takes an hour and a half, but having a place to stay in Paris makes for a mini vacation rather than a day trip for them.
I found Lena's studio on AirBnB.com a site I have used before for rentals here in the US. Pour mes amis Francophone, vous pouvez aussi louer le studio avec amivac.
Lena's studio is in a perfect location between the Jardin du Luxembourg and Jardin des Plantes, just a few minutes walk from the RER B which goes directly to Charles De Gaulle airport. For less than $100 a night, this very secure, quiet studio is a steal. The popular Rue Mouffetard is only two blocks away with wonderful restaurants and shops, and the apartment itself faces a green courtyard. Lena speaks English perfectly (as well as Italian and of course French), and uses this studio as her office, so everything is immaculate and functional. There is free wifi and the phone can be used to call several countries landlines (not cell phones), so this is a real home base.
At 35 square meters, this is easily double or triple the size of many hotel rooms in Paris and you get the added convenience of having a full kitchen with a refrigerator, microwave, sink, two burners, appliances (toaster, coffee maker), cutlery and dishware. The pleasure of buying baguettes, cheese, fruit, and wine is matched only by the ease of having a place to prepare a snack or meal should the mood strikes you.
The bathroom is huge (by Parisian standards), with a full size tub, good water pressure, and even a selection of shower gels and shampoos. Lena supplied all the towels and sheets for the fold out futon in the living room, so aside from maid service, her studio has everything and more than a hotel room.
Lena was very organized, sending out information about the area (her favorite markets, restaurants, transportation details) as soon as I booked. I enjoyed her place and Lena so much that we talked about trading places next time. Since her full name is Helene, we even have the same name (Elaine in French is Helene), so we wouldn't even have to change the answering machine!