There are some great suggestions in this article on how to save money in the City of Light. Many are the obvious with lots of picnics and cheap enjoyment of the outdoor museum that surrounds you. However, the issue isn’t whether it’s possible as a parlor stunt, but how could you have a fulfilling Paris experience while skipping most of the things around you.
It’s hard to imagine a once in a lifetime Paris vacation spent entirely outside while trying to avoid museum fees, but there is a free Sunday of the Louvre. There are plenty of places to go (Tuilleries, Jardin de Luxembourg, Notre Dame, Sacré Coeur) that don’t cost a dime.
Best advice if you really want to stick to this budget: get a hotel outside the city on the RER line and zip in in the morning and go back out to sleep. Basic hotel rates will eat the majority of your budget if you stay within the city limits.
Paris on Less Than $100 Per Day