There was a KOA just down the road from our house. It's a resort called Bahia Escondida on the Presa de la Boca. Huge timeshare and they opened the KOA right on the water.
It's no longer a KOA but the cabins are still rented, the showers and laundry were in good shape last time I went to check. I don't recall if the power was 30 or 20 amp but many rvers stayed there over the years.
It's now about 600 pesos a night but you can usually talk them into a 2 for 1.
There are some wonderful non-developed state parks throughout Mexico and we have used many. Some have palapas with electricity and some with very strict rules such as lights out at 10 p.m. and purposely without electricity so as to keep the music down.
Some good national parks as well and Sierra de Organos comes to mind. I am not or have not been a big fan of iOverlander as there are lots of places I wouldn't stay overnight such as a PEMEX. But this last week I have been checking and there are some interesting places. Quite a few around San Cristobal de las Casas for one.
It's almost time to get back on the road, two more weeks and we get the second jab here in Nuevo Leon. Of course we do it differently in the north, we don't listen to the federal government we do it our way :)