hello, I will be in Paris in Sept. looking for prime areas to stay in and cheap accomodations.
i know Paris has affordable hotels however, what are your recommendations? my budget is less than $150/night.
thanks
Amy

Each person's prime area is different, although there are tendancies according to nationality.

I think that your budget will allow many choices. This question gets asked about once per week on this board and ,if you do a search, you'll find lots of information!
To be brief, one starting point would be to look at accor.com, which would give you information about a chain of hotels of various price levels, with locations. Often, rates are better if you book for several nights, or look for lower rates at some hotels on weekends.
There are many posts that describe non-chain hotels, and will give you advice about neighborhoods. Rates can be lower if hotels are relatively far out from central Paris, but be careful to avoid spending too much time commuting!
Within central Paris, I'd say that there are no really dangerous areas, but there are some that are seedy--- Pigalle, and rue St Denis, for example, have strip joints.