Stayed here a little while back. Whenever my friend came out to San Diego to visit he was always on a mission to go to Vegas even if it had gotten a little played out in my opinion. Well due to my college student poverty and the inflated prices due to NASCAR weekend -- a real treat to see mullets, cutoff shirts, & chewing tobacco spitting juxtapose with the pomp and circumstance of regular visitors -- I had to seek out the cheapest lodging option.
I accidentally booked a weekend in May instead of March (Doh!), but the lady was very accommodating when I called her and was happy to change the date without any incident. They supposedly have 2 tent spots, but they were full. The lady again was very empathetic and said that there is an open parking spot in front of her RV (where she lives while working there) and a large grass median on the side that we could pitch our tent. It could've been a little bit wack having to stay on the median, but it worked out fine and I appreciated the helpfulness. This KOA is perhaps not on par with the mini-resorts you'll find elsewhere, but it's not a bad place to plop down on a budget.
Second cheap option is to stay 35 miles out in Primm, NV and pay $20, but it's a hell of a lot easier to stumble back to your tent/RV on the strip than make it back there!