If you buy a $15,000 car and a $50,000 car, the latter is going to be made with higher quality parts, better craftsmenship, etc.

Generally you are right. However, in my experience a $9,000 Hyundai is better built than my grandparents $40,000 Cadillac Fleetwood Brougham. Before it was discontinued, they bought a new white Fleetwood every 2 years. Their current Fleetwood and previous Fleetwoods probably had more vertical miles than horizontal miles (get it?... from going up and down on the lift). Another example of crappily built expensive cars is Jaguar before Ford bought them.