It sounds rediculous, but that's what most places charge up that way. I came down from Bar Harbor to Philly after crossing the country. I don't recall any cheap camping except for maybe a state park outside of Freeport, ME, and that was in '99.
This spring I did a 3-day on the ACA route from Port Jervis to Philly. I camped at a commerical place on route just south of Port Jervis. The owner gave me a price break because I was on a bike. Think he charged me $15. The campground at Worthington State Forest on Old Mine Road is a great place to stay, and the ride there from Port Jervis is sweet. $25 for non-NJ residents. While there are almost no services between Port Jervis and the campground, you can drop your gear and ride the relatively short distance into Delawar Water Gap, PA. There is a diner and pizza place there along with a couple of other more expensive places to eat. No grocery store, but there is a C-store with limited selection of groceries. I would not recommend stealth camping in the Delaware Water Gap Nat. Rec. Area unless you take serious anti-bear measures. There are a lot of them up that way. Worthington in on the AT so there are group sites with bear lockers. An employee there told me they would never turn a cyclist away, so no need to make a reservation.
I also camped at Dog Wood Haven on Lodi Hill Road on the PA side of the river across from Milford, NJ. (The campground is listed on the map addendum now that Bull's Island campground is closed.) The owner is a nice guy. He also charged me $15 since I came on a bike and offered me a beer. The local grocery/liquor store in Milford may not look like much from the outside, but it has a good selection of groceries. And the pizza place in town is good.
In theory, you can stealth camp along the D&R trail between Frenchtown and Stockton, but you have to look carefully for s spot as the area between the trail and the river can be rocky, overgrown and/or not level enough for a tent. South of Stockton, things get a little more developed, but I can see maybe fiding a secluded spot if you look hard enough. Forget it once you hit L'Ville as the trail runs behind houses and right against the canal.
Send me a PM if you would like more info. on this part of the route. BTW...I was just in the Summit area on Sunday. Our club does an annual ride from New Hope, PA to Cobble Hill in Brooklyn.