I'm 60 years old and I've only bought 2 cars new in my life. I think a used car in good condition is a much more cost-effective option.
I don't know where you live so I can't be too specific, but I'd just search for "used cars", "cars for sale", and the like on the Internet. There are plenty of web sites out there for used car dealers, and sites where private sellers can post cars they have for sale.
I wouldn't go looking for a particular make and model. Just search ads or postings and see what's available in your area.
A lot depends on how much money you have to spend. If all you have is $100, well, I guess you have to buy a $100 car. I wouldn't expect such a car to last long.
A fact of life with used cars is that you can't be entirely sure what you're getting. The odds are that it will turn out to have some sort of problems. When I buy a used car, I make sure I set aside some money to repair anything that might turn out to be wrong with it. Last 3 used cars I bought I set aside $1000. That is, if I have, say, $5,000 available to spend, then I say I can spend $4,000 to buy the car and I put aside $1,000 for repairs. Then I'm prepared both financially and emotionally. If ... when ... some problem turns up, I have the cash to fix it. And I don't freak out that I've been cheated and the world is going to end.
I bought a car for my daughter, wow, probably 10 years ago now, that cost I think $3,000. It had some serious electrical problems that cost about $1,500 to fix. I thought that still ended up a decent deal. A year or two ago the problems started to multiply and it was time to retire it. She has a decent job now and while I helped her out a little, she mostly paid for her own car. She spent about $10,000 and got a "certified used", which is another option. Used but has a warranty. You pay for the security, but it may be worth it.
On the other hand, a few years ago I bought a pick-up truck for $5,000. It quickly needed a new transmission, new transfer box, major front end work ... and then the engine blew up and it needed a new engine. I debated dumping it or replacing the engine, ended up paying $4,000 for a new engine. In the end I paid like $15,000 for that truck. I've got some decent use out of it so it wasn't a total disaster, but I considered new at the time and I found I could have gotten a new truck that had the features I wanted for about $17,000, so buying used in that case turned out to be a mistake.
But the thing is, you don't know.
Oh, I should say that I have some modest mechanical abilities. I can replace spark plugs and I've replaced starter motors and alternators and put on a new muffler and that sort of thing, but that's about as far as I go.
Side note: It can really pay to learn to do some work yourself. Like a month ago my son's car had trouble, mechanic said the integrated power module needed to be replaced and that would cost $1500. I said forget it, bought a refurbished one for $100 and put it in myself. Turned out to be a very easy job, my son and I did it in less than an hour.