Here's the link to the Port Autority bus to AC. I take it a couple of times a month, getting on at the stop it makes in NJ. These are decent commuter buses, but not charter bus quality. You can take any of the return buses you want. You aren't locked into returning on the same bus that brings you down.
One caution - sometimes scheduled return buses fail to show, or are full. Then, you have to march to a different casino to get a different bus. This has happened to me about 10% of the time.
http://www.academybus.com/