Hi, and welcome to the forum. I should also probably say, "welcome to Paris!" As you've discovered, accommodation is terribly expensive in the City of Light. You may want to consider finding a place outside Paris, closer to Roissy. Rents are more reasonable outside the city, however the suburbs to the north include some of the "rougher" areas, so be careful.

To look for a place to stay (especially a short-term rental), you should check the FUSAC website: FUSAC - Petites annonces pour anglophones de Paris

FUSAC is a free want-ad magazine that is available in lots of English language shops and bookstores in Paris. It's extremely useful for finding short-term rentals and sub-lets. The "normal" lease term in France is 3 years, so chances are you're going to be looking to sub-let for the shorter term. Lots of people also combine resources and find roommates to share costs.
Cheers,
Bev