Average rent in San Diego is $1,630, NYC is $2,000, and the average per month cost of a car is $430 a month. Average collision insurance in San Diego is $440, and California's gas prices are about $2.80 gallon. Thirty day unlimited Metro Card is $113.
So $2,113 a month in NYC,
$2,500 $2,096* (not including gas) for San Diego. So not really impressive, considering one is still New York and the other is San Diego.
(* It's late, I did the math wrong.)
Your math is way off. Median 2 bedroom apartment rent in San Diego is $1795/month. Median 2 bedroom apartment in NYC is $3500/month. Average car payment per month for a new car
is $479. A used car will be much less expensive (but may have other expenses attached). Gas depends on how much you drive, obviously. But if we assume an average of 12,000 miles per year, that's 1000 miles per month, which at 22 average mpg works out to about 45.5 gallons of gas, which at $2.80/gallon works out to about $127/month for gas (um... not much more than the metro card, but usable 24 hours a day and not just until midnight).
Insurance should bake out to less than $100/month. Driving in San Diego is still much much less expensive than taking the bus/rail in NYC. And this assumes that all of your transportation needs can be met with the metro system.
Of course, one you've paid of your car, the only expense is gas, insurance, and maintenance. Which, while certainly more expensive than the cost of a monthly metro pass, is far far more convenient. I'll gladly pay an extra hundred bucks a month or so to have a 10 minute commute rather than 1 hour, and be able to bop over to any store or restaurant or whatever whenever I want for any reason I want. Or run over to a friends house at any time of the night or day without having to think about bus schedules and transfers or worrying about how I'm going to get home afterwards.