I want to buy a cheap clunker. What things are essential?

I’m in the market for a piece-of-shit van that I can spray paint all hippie-dippy and take to Burning Man. I need for it to get me 3.5 hours away from my town to the high desert in Northern Nevada salt plains and back. I intend to donate it to charity as a tax write off almost immediately after Burning Man.

When looking for a cheap clunker, what things are vital in order to not waste my money or have a money pit? I’m hoping to spend around $600—$800 total, and expect it will be a 78–80s year…

Cosmetics aside, what specific things should I pay attention to when shopping? Please don’t be so generic as to say “an engine” or “one that runs.” I imagine something that old and cheap will have issues, I just don’t know the difference between a major issue and a minor one. Think mechanics, as one that old won’t have a lot of electronic components. Thanks!