Guys, you are right about the unfortunate situation with private land ownership. $76 does not match my definition of "primitive camping." Would we were as enlightened as Scotland, where there is a "right to roam" law.
On the South Fork of the Shenandoah, much of the land on river left between the Inskeep and Bentonville public landings is National Forest where camping is permitted at no charge. This river is heavily used and close to DC. Sites where there is motor vehicle access can be heavily impacted, but except for those spots you should be able to find a decent campsite. In addition, the Shenandoah River State Park just downstream from Bentonville has a canoe-in campground.