Cheap hotel (priceline) or the YMCA?

I am planning on visiting NYC sometime in the spring, so I started looking at places to stay. I would really like to keep it under $100. I figure I won't be in the room much, so I don't want to pay much. Also, I would prefer to be in a nice location (i.e. Manhattan). Is it possible to get a room in Manhattan on priceline for under $100/night? If not, what about the West Side YMCA near Central Park or the Vanderbilt Y? I won't be in my room much, so all I really need is a clean, safe place to sleep at night.