I put Penn Station to Parx Casino in Google Maps using Public Transportation for the hell of it. This seems to be the simplest and might also be the cheapest way:
- At Penn Station, take the Acela Express (Amtrak) towards Washington Union Station (1 hour, 5 minutes) to 30th Street Station in Philadelphia
- At 30th Street Station, take the MFL (SEPTA Train) towards Frankford Transportation Center (26 Minutes) to Frankford Transportation Center
- At Frankford Transportation Center, take Bus 50 to Parx Casino (50 Minutes)
Of course there is waiting involved depending on what time you are going. But this seems painless and doesn't leave for a lot of walking in possibly unfamiliar areas.
As for the cost, Amtrak is $53 each way and you can take SEPTA for $3.25 ($2.25 + $1 transfer) though you can save a little bit buying SEPTA tokens for $1.80 each.