There is a 14 day free area west of the Pilot Knob LTVA. But it's about 3 miles down a dusty dirt road. Go to the LTVA entrance at the Sidewinder Rd. exit on I-8, then turn right just before you enter the LTVA (you'll run along the LTVA perimeter fence). Don't take the paved frontage road - you can't get to the free area from it.
Personally, I'd rather just pay the $40 LTVA fee and stay there, especially if I will be going in and out more than a couple of times. The LTVA is on high ground and has a hard packed solid surface, while the free area is lower and much sandier. The LTVA fee covers a two week period and gets you into any LTVA during that time, something to consider if you're going to Quartzsite or elsewhere in the area.
Water (halfway decent well water and R.O. filtered drinking water) and a dump station are available for a fee at the Shell gas station near the LTVA entrance.
Or you can boondock in the lower parking lot in the casino at the Algodones exit (I think it's something like $5 a night) or on the Indian land along the Algodones road or to the north of the freeway. A tribal representative will come along at some point to collect the fee.