Good question. I've found it somewhat difficult to get to an exact number given the wide variances in types of vehicles. We have one vehicle now and so estimating for a second is a less than exact science. That said, we'd be looking at 40-50 miles per work day RT and then the cost of the vehicle, maintenance, insurance, and registration. I found the $600 in an article online and it seemed like a reasonable average. You think it's too high? Or, too low?

It seems too high to me, but now that I see you found it online, I get it. However, just as you can optimize the work->retire flowchain and ER, you can optimize car expenses too. Off the top of my head, here are some rough numbers from a friend of mine...

$100 ($7.2k for a car kept for 6 years)

$20 (Minimum insurance at $240/yr)

$100 (Registration, maintenance, etc at $1200/yr)

$72 (24 mi / d = 120 mi /wk = 480 mi / mo, 24 mpg = 20 gallons * 3.60/g = $72/mo)

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That comes out to $292/mo, and to be honest, I could have decreased the number more. The biggest factor isn't gas (the commute length doesn't really matter except for the time, stress, and danger it adds), but the initial cost of the vehicle. If you buy something expensive, your monthly costs will be much higher unless you drive it into the ground. If you start with a cheaper vehicle, the numbers are much nicer.