If you buy a used car, it will run into problems. If you go to a mechanic with even the smallest of problems, they will quote you $500
I think that you perhaps have a lot to learn about cars.
EVERY car has problems. They're mechanical things. Mechanical things break and wear out. If you're smart, and buy reliable things like Toyota Corollas, etc, they have very very few problems. If you're insistent on buying notoriously unreliable cars, then you're likely to have more problems. The idea that new cars are problem-free is absurd, and it's not likely that paying the huge new car price just to avoid paying potential mechanic's fees is a financially smart move, ever.
I don't know what kind of "mechanics" you go to, but I haven't had a +$500 repair in well over a decade. It sounds like you're A. buying bad cars and B. don't know enough about cars to know if a mechanic is ripping you off or not.