My husband and I stayed at Residence St. Nicolas when we were looking for a permanent place. The residence is located right by Part Dieu, a city center-ish area and has great access to anywhere in the city. It was the most affordable option we could find in that area, but it still came to 45 euros a night for us (this is with discount through my husband's work)...However, by the time we were leaving, they offered to let us rent the room (one bedroom w/ kitchen/livingroom apartment type) for 650 euros a month. Anyway, sorry for being long-winded, the bottom line is that perhaps you can talk to these apartment-hotel places and ask for a (big) discount if you rent for a month or longer. Best of luck! And check out paru-vendu website. It has lots of ads. Also, there is the Centre Régional Information Jeunesse CRIJ...I have seen quite a few students coming there to look for places. It's a youth center but all age groups are welcomed. People there are very nice and the place is nice, safe, and clean if you're just looking for some place to camp out for a few hours.