Do most people who live in Tokyo own a car? Or do they use train, transit etc.?

Question:

How much does a decent car cost compared to buying one in the states?

Answer:

Most people don't own a car. Most use public transportation.
Cars are very expensive to own. Last I heard gas was over $6.50 a gallon. Probably higher by now.
Maintaining a car in Japan is much more expensive than in the US.