[Sleeep]

This is incredibly specific to an individual, so specific that the math would have to involve an algorithm with probably 15+ inputs.

Consumer Reports and the like have calculated "true cost of ownership" for different model cars you can use as a rough guideline. They estimate depreciation, taxes, financing, gas, maintenance, and insurance over 5 years. However, that's just a rough estimate and only a first step, it doesn't take into consideration individual variables. If you are a young male, have to drive in stop-and-go traffic every day, and pay to park everywhere your cost of ownership will probably be close to double.

Auto insurance alone is probably close to $100 a month for the average American - depending on your car, location, and driving record, of course, I'm just making an educated guess. IIRC, last I ran the numbers with my car (average budget model) cost of ownership was around ~$20,000 over 5 years. That's amortized to $333 a month.