There's been some discussion over at the California High Speed Rail Blog about the cost of the system. Basically, a Freakonomics guest blogger threw around the figure of $80b for the system, which is considerably higher than the forecasted $40b. No one really knows how much the high speed rail system will cost, but the numbers everyone quotes need to be contextualized. In other words, much did the Interstate Highway System cost? Per person, and adjusted for inflation? Was it considerably more than high speed rail?
According to the wikipedia site about Intersates, the highway system cost $425b (inflation-adjusted) to build over a period of 35 years. In 1950, the population of the country was 150m, and in 1960 it was 180m. So, in 2007 dollars, the Interstate system cost about $2500 per person alive at its inception (425b/165m, the approximate population when the highway system was funded, in 1956) to build. Per year, it cost about $75 per person.
California has a population of approximately 37m, and we can assume that the final bill for high speed rail would come in somewhere in this $40b to $80b range. Running these numbers, California's HSR system would cost about $1100 to $2200 per person, spread over a period of about twenty years. Per person, it would cost less than the Interstate system—perhaps considerably less. Per year, it would be between $55 and $110—quite comparable to the Interstate system.
There is one minor difference between the Interstates and High Speed Rail. Say what you want about CAHSR's business plan, but as far as I know, the Interstate Highway System never had a business plan which showed the system making a profit.