Part of being born in America and not having a very intelligent parent to guide you through involves being an easy target for an ever growing and complex series of grifts.
Of course at some point someone saw dollar signs and the rest is history.
When I was homeless in North Dakota I met a guy with a Ford E350 ho bought for about the same price. He was handier than I was and as far as I can tell he could keep it running indefinitely from junkyard parts for almost nothing.
The grift is overselling what goes into the van, or a new and overbuilt van. The bigger issue is van-life dumps your externalities on everyone else -- you aren't paying property taxes but you probably still avail yourself of local public services and utilities as part of the cheap living. It doesn't scale.
This was in 02006 so add 50% to all these numbers; the dollar has lost a third of its value since then.
https://www.flickr.com/photos/blmurch/129519600
But we also drove about 10000 km during that time, a quarter of the way around the world, and that was the expensive part; something new would break on it every day. And the auto transport was a big expense caused by needing to meet a deadline even though I still had the engine apart. (The first time I paid someone else to rebuild it; the second time I did it myself.)
There were three weeks we were parked in a campground with a cracked cylinder head when I think we spent about US$600. If we'd been driving 30 km once a week, or 3 km every day, instead of over 100 km a day, and if we hadn't abused and overheated the engine, it would have been a pretty cheap way to live. I don't know if we could have gotten below US$100 a month but I think US$300 would have been within easy reach.
And it was the most pleasant place I've ever lived, but it didn't have a toilet. There wasn't room. But it had a propane refrigerator, a stove, a sink, a bed, storage space, a pop top, and a propane space heater.
That was 16 years ago, I think cars are better quality now. Finicky air-cooled engines are few and far between nowadays — the guy who bought the van from us sent a rod through the crankcase a few years later after driving 100km down the highway in second gear — and cars generally have better metals, more sensors, and less risk of bursting into flames.
If you were just looking for something that would safely provide shelter you wouldn't need something that was the most pleasant place I've ever lived. One night I slept in a Wal-Mart parking lot on an airbed in the bed of a pickup truck with a hardtop. https://sfbay.craigslist.org/eby/ctd/7553195670.html is a 23-year-old pickup with hardtop for US$8000, with a 2.5-meter-long bed, and it's a Toyota, so you wouldn't have to fix something new on it every day.
Oh, about toilets. Piss is easy enough to manage in Gatorade bottles but shit requires more care. An ecovillage I used to spend a lot of time at, years after the Vanagon, used 20-liter plastic paint buckets for the shit. After shitting in the bucket you would throw in enough wood ash to raise the shit pH into a sterile range and also increase its osmotic pressure into a sterile range, preventing fermentation either aerobic or anaerobic, similar to a chemical toilet. They didn't keep the shit buckets in the living shelters but there was so little smell that I think it wouldn't have been a problem as long as you never spilled one. Later they switched to composting the shit, replacing the ash with dry leaves, which are reasonably effective and easier to get. I have used this solution, with the addition of a black garbage bag, when housesitting for a friend whose toilet was broken; at least over a short period of time there is no smell. These buckets cost US$6 new with a totally airtight lid.
For hygiene, we had wet wipes, rubbing alcohol, and clean cotton clothes. It's surprising how far those can get you, even if you aren't stopping in at truck rest stops and the houses of friends and relatives.
I am actually empathetic to children raised with dumb parents and yuppies who were grifted into selling their belongings to follow the tiny life trend.