In case you missed this AP story by Joann Loviglio, she covers many of the things you can do and places you can see in Philadelphia for no cost at all:
The City of Brotherly Love is perhaps best known for its Colonial roots but locals will tell you there’s much more to explore in this city of 1.5 million people. Options abound for travelers looking for free things to do in and around the historic district and beyond — and they don’t all involve tri-corner hats and Betsy Ross’ flag.
It’s a short walk from the city’s most popular tourist attractions to several Philadelphia neighborhoods and shopping districts, which abound with shops and galleries that provide plenty of eye candy for browsers and window shoppers even without opening your wallet. Farther afield is the city’s prestigious art museum, which boasts glorious views from its famous steps. Free options for the outdoorsy include a lush wildlife refuge south of the city as well as Fairmount Park, a 4,100-acre (1,660-hectare) jewel of trails, streams, historic buildings and public art.
The full story is worth a read and will give you some great ideas for how to explore and enjoy Philadelphia at a minimal cost.