Not sure what constitutes "low cost." Free is nice. I think anything $20 or higher I would consider out of the "low-cost" bracket. Anything under $10 I would definitely consider low-cost. It's that $10-$20 range that's questionable.
And that is where a lot of the state parks in the area fall. Many non-electric sites in the area go for $15/night: Jordan Lake, Umpstead, Falls Lake, Kerr Lake, Medoc Mountain. I have not been to all of those, but the ones I have visited had a bath-house, toilets, and water. There are some more primitive sites at Jordan Lake with pit toilets and water, but no shower for $13. There are some hike or float in sites in the area that I'm not certain of the facilities at Raven Rock and Eno River. At Raven Rock I remember a toilet, but I can't remember the water situation. I do remember having to park the bikes at the office and walk a good ways carrying panniers. Haven't seen the campsites at Eno. I think they are "hike in" as well. Those sites are $10/night.
NC State Parks
The Uhwarrie National Forest is long day's ride (for me) from here, and it has established, paid sites, but I believe also allows free, dispersed camping.
https://www.fs.usda.gov/recarea/nfsn...49832&actid=50
Neuseway Nature Park is also a good day's hike, but it's only $6/night for tent camping. It's also interesting for being right across the river from downtown Kinston, NC, so you have access to the amenities of a mid-sized town while also being able to camp.
Campground | Kinston, NC
The other one I know of in my area falls into that grey area. No amenities. Unofficial. But not exactly secret. I think it's the kind of thing tandempower was talking about. I camped there once, and some other campers showed up after I did. When you're there, it's clear that people have been camping there, and there are no signs forbidding it, currently, but I do believe it's private property. And someone woke me up in the wee hours who seemed to be "policing" the area, but whether or not they were actual police, I don't know. They didn't ask me to leave, just verified that I was camping for the night and went on their way. The other campers' tent was still there in the morning as well, so presumably they had not been kicked out either. I camped there because it was conveniently located for the trip I was on, but other people seek it out for more arcane reasons.
https://en.wikipedia.org/wiki/Devil's_Tramping_Ground
That's everything I know of in my immediate area (i.e. a day's ride) in the 0-15$/night range. Only one is actually free, and it's the one I'd be the least surprised at being denied entry or asked to leave. Or chased out by evil spirits, if you're into that kind of thing.