How do I get from penn station ny to the central islip holiday inn?

I am taking the amtrak from Illinois, to Newyork penn station, and I was wondering how about would I reach my final destination, which is the holiday inn, in central islip ny... is there a certain bus/subway id take? and being id be there at penn station at 8:40 PM, would busses and subways be running and how much do they cost to ride to my final destination.