Try reserve America, state parks are a great place to stay and cheap, there are a few located in the Catskills and Berkshires. Most CGs in the northeast have 2 sets of rates in season and off season. If want to save on fees, then you need to look farther from your target area. If you end up staying farther out, you would end up spending more in parking fees and tolls. plus traffic time.
The DW and I went down to the DC area last fall to do some sightseeing. We could of stayed at 1 campground who was close to the metro area, but was pricey. We opted to stay at another farther out. We brought our toad and after setting up, went into DC. Stayed 3 days and went to DC 2 of them. Saved on fees. What we saved in CGs fees, cost us time sitting in local traffic the majority of time.
Moral: We went with the object of enjoying our sightseeing of the national mall and other landmarks. End result was spent majority of time sitting on city streets in heavy traffic and spent very little time sightseeing.
campground A was 20 miles out, the one we stayed in was 50 miles out.
Good luck, Catskills are great with lots of thing to do, many CGs usually have openings for the upcoming holiday. The city can be exciting unless you live within 100 miles,(maybe further)
