OP, it's too bad you can't head west to the middle of the country. I've been mapping my route for an upcoming trip and when looking for an overnight CG in mid-Kansas I found a number of $10 campsites along the route. Some include showers and water/electric. A couple of the municipal CGs in towns I'll be driving through are free (no amenities, though).
Iowa and Nebraska have plenty of affordable campsites in the $10-$30 range, too. And the NF CGs at my Wyoming destination are $10 as well.
East coast real estate is expensive, so maybe that influences the CG fees.