There is a train from the airport in Philadelphia which takes you directly into Center City. This takes about 25 minutes and is $5, maybe less for students. Take the train to Penn Center Suburban Station (which is not suburban at all but probably was when the station was established). This puts you across the street from the Philadelphia tourist office on JFK Drive. Here you can get bus tours around the city.

To find individual bus tours try: http://www.gophila.com/itineraries/ Go here and then under 'Tours' try 'Bus &Trolley'.

A cheap option is a bus called Philly Phlash. This tourist bus makes a continuous circuitous circuit around the city. Check it out at: http://www.phillyphlash.com/

Have a nice trip, Jude