Re: NW Pennsylvania
If you're going to do the Steelie thing(which is wrapping up soon), i would recommend Folly's End Campground. There's a good fly shop on site and it's very inexpensive. Last year I paid $16 a night.
Other than Steelies from Erie and the Allegheny NP, there's not a lot that I know of in the NW of PA. If you want to wander into central of eastern PA, send me a PM and I can give you a bit more info.