I was doing a search for transportation for AC, and I came upon this thread. I wanted to add that there is a Greyhound bus that travels from PHL to AC for $30 roundtrip if you prepay on the Internet, or $40 roundtrip for a refundable fare. It looks like the trip back is open so that you can change the date of the return trip if needed without paying a penalty.
http://www.luckystreakbus.com/