Computers aren't regulated nearly as much as cars are, which cuts down the price a lot. That is not to say cars aren't regulated for good reason, though. Apart from emissions control (which is a significant expense), the numerous safety features required in modern cars add considerable costs. Research and design also aren't free--it costs a lot of money to design a car, certainly much more than it used to, and those costs have to be defrayed in the sales of new cars.
Of course, one could also blame unionized workers, whose pay has fared better against inflation and wage levels as a whole when held up against non-unionized workers (the vast majority of those who will be buying cars.) By that token, cars seem more expensive because, in real terms, most people's pay has stagnated or fallen.
In short, I don't think the current price of a new car is generally unjustified, considering what you get for it. Even "base" model cars have a lot of features that absolutely weren't standard 20 or 30 years ago: airbags, air conditioning, power windows and locks, CD/MP3 player, anti-lock brakes, electronic traction control, etc.