Telsa cars are expensive for the same reason Ferraris are - they target people who want bling.

A mass-produced commuter could be much cheaper, but there's a huge risk. Tesla aims to reduce the risk by validating the market, solving technical problems, creating infrastructure (recharge stations) and solving social problems (convincing people that range doesn't always matter, and educating them on the strengths and weaknesses of electric cars).

A low total-cost (including fuel and maintenance) electric car can probably be produced, but it's not the Tesla's top model.