IIRC I spent about US$6000 (not US$60k, US$6k) on a 24-year-old Volkswagen Vanagon with an aftermarket camper conversion kit. My wife and I lived in it for about three months as we traveled around the US visiting people. We had to rebuild the engine twice and are damn lucky it didn't catch on fire due to a copious fuel-line leak, so we spent about US$10000 on repairs, gas, renting an auto transport, renting an alternative car, etc., and I think we sold it for about US$4000. So in a sense we spent US$12000 on three months' rent, which is quite a bit more than we were spending on our apartment in San Francisco.
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.