I keep my cars for a long time. I bought my last Expedition used, a lease back, in January 2010, with 34K miles. I paid ~$28K plus tax, so close to $30K. Sold it for $7500 in May of 2018. So, $22500/100 months, or $225/month in depreciation. But, the previous owner hadn't changed the oil enough, the dipstick had varnish on it, crap from kids under the back seats, etc, etc. I did the math at the time, the cost of ownership to 200,000 miles wouldn't have been much different than if I'd bought a new one. Of course, the numbers get bigger with each passing year, but I think depreciation worked out to about $0.22/mile. If I keep my new one for 12 years/200K miles, and sell it for $10K, I will have paid $48.5K in depreciation, or $336/month, or $0.24/mile. I look at long term cost of ownership, buy new and drive them a long time.
No used cars for this guy, it's not worth it to me to put up with previous owner's crap. If you can keep your cost of ownership to $100/month, more power to you. It's instructional to look at the 5 year cost of ownership from Edmunds, etc.
BTW, what was your last car? By cost of ownership, you're just talking depreciation, right? I probably pay $100/month just for fuel.