Parking at PHL is a lot more difficult now that SouthWest is entrenched. The lots (and the hotels) are MUCH fuller. Thankfully the parking rates have not increased too much, the hotel rates have though.
Most people going to PHL from the DE or MD area use the parking lots west or south of PHL. Most people I know from DE use Ramada, Priority or Colonial. I prefer Ramada and if full, I just procede up RT 291 until I find an empty lot. The price gets higher as you get nearer the airport.
MisterNice