No, there are no official free camping sites in Ciudad Constitucion. The paid RV parks are a fairly affordable option, though, and the extra amenities are ACTUALLY worth it versus some of the more run-down paid sites in remote Baja destinations.  You may spot some people boondocking (or setting up camp in secluded, unregulated areas) but this is not recommended here. You’ll be much safer sticking with a larger group of campers and juggling your camping budget to accommodate an RV park stay.