Either drive through a small town and look for "For Sale" signs (old people ain't selling online)
Or hit up the Goodwill or Police Auctions - most major cities have them once or twice a month.
SUVs and Work Vans are the high ticket items that get a crowd of bidders (3000 and up), but you can score a nice sedan for under $1000.
Police Auction is kind of hit or miss cause someone who got their car towed, if they couldn't fork up a couple hundred to get it out of impound they also probably neglected maintenance. Plus most of em don't come with keys, so there's a locksmith onsite who will cut you one for $100.but if you want a wireless keyfob you have to go to a Dealership and have one made.
The goodwill Auctions are the same price range, but the cars older (2000-2010). But they come with keys, and we're generally owned by "well to do" people that kept em in garages. They generally give a heads up what's wrong with it, like it needs a battery or fuel pump. I got lucky a couple times and just had to pump up a flat tire and was able to drive off (though I ended up buying all brand new ones, cause they were 10 years old)
In the rural areas, they tend to be 1990-2000 cars that the elderly person bought brand new and has meticulously maintained. They might have run it up 50,000 miles during their first several years of ownership, but once they retired they only put less than 1000 per year (driving to church).
Estate Sales are another option, it's like the concept of a yard sale but everything I. The hiuse (and garage) is up for grabs. These are generally collectible/sports cars, or older 1980s. I ended up grabbing a Porsche for $4500. Had to take it to an upholstery shop to get a new convertible top which set me back another 1500. So the first year I would only drive it once a month (to keep the battery and fluids stable). In the 2nd year when I was able to afford a water pump/timing belt and started driving it once a week. This Summer I'm setting aside money to get the suspension done and will be driving it damn near everyday.