You don't say where you are starting your trip, but you mention the Chinatown bus so I'm gonna guess NYC...and I can't help you.
If you are taking the SEPTA R1 from Center City Philly into PHL, the cost is $6 if you buy at the station and $7 if you buy on board the train (o/w). It looks like the earliest R1 will get you to PHL just before 5:00 am (I've taken early R1 trains and they have been late) so be careful about the timing.