You sure about that? A $7k car expensed over 18 months plus insurance and road tax is ballpark $450 /mo. That omits maintenance and fuel but conversely also underestimates how long the vehicle will be kept on average. Depending on where you live parking will range from free to potentially more than $100 /mo.

If you manage to stretch $10k cars out to 5 years on average with zero maintenance it's less than $200 /mo but ... no maintenance in 5 years?

I think $300 /mo plus fuel and parking is probably a reasonable estimate for frugal behavior.