Should you buy used cars or new ones? The moment a new car leaves the dealership it's value falls. That makes the question a lot simpler to answer. Since a car is a depreciating asset, meaning in general cars lose value with time, the best money decision is to purchase the car when it will tend to lose less value. Balance that with the time when the car won't need as much repair work. Those states converge in the slightly used car. The value has already dropped from new car state. That loss went to the original owner. The car likely won't need constant repair work, and the warranty is still probably valid.
Late model used cars are available from a variety of sources. Dealerships take in trade-ins from customers who purchase or lease new vehicles. The dealers want to sell those cars. Companies like Carmax specialize in used automobiles, while eBay has an entire subsection dedicated to car auctions, mostly for used vehicles. There are car auctions in every city. These include police auctions of impounded vehicles as well as dealer auctions that might involve, for example, cars purchased from car rental companies.
Kelly Blue Book is a valuable resource to determine the relative fair price of a used car. Categories include make, model, year and condition from poor to excellent. It also breaks down the prices between dealer sales and private sales. That does make a difference because dealers have overhead that private sellers do not have.
Have you considered financing? First consider paying cash. No matter how low of an interest rate or how low the monthly payments, nothing helps the monthly budget like not having to make any car payment. Yes, cars are status symbols. But bells and whistles can cost a lot of money. That not only helps your bottom line, but your blood pressure. Theft, wear and accidents are bigger worries for people with fancy cars. Many used car owners take pride in their cars, but don't worry over a ding or two.
Wealth isn't made by spending, even on a car. Net worth comes from saving. Saving turns rich people rich. Good used cars help the budget.