Real "bottom" for non-shared apartment in Shanghai is ~3000 rmb (~$500) for a smallish place with a 1+ hour commute. Rents in the downtown are around 10000+ rmb.
I paid 1600 RMB per month for 18 m² in Minhang, fully furnished, with cooktop in a corner of the living room and own bathroom. Your "bottom" is not the actual bottom. Those places for 1000 RMB or less are super tiny (as I said, the size on the listing is exaggerated), but they do exist.