[snip scenarios for brevity]
You would have to run the crap out of a car to have it be worth $0 after
10 years. Bankrate shows a car loosing 15% a year, so the cars would be worth about $3K at the end of their lives in your examples.I'm using your 8% opportunity cost, but I'm coming up with higher numbers. It seems I'm taking compounding into account?
Now the numbers are more like:
$17K car. (cash, kept for 10 years) depreciation: $13,700 (15% value loss per year for 10 years.) Opportunity cost: $21,000 ($17K earning 8% for 10 years.)
Cost over lifetime average: $3,500 per year
$7K car. (cash, kept for 5 years) depreciation: $3,900 (15% value loss per year for 5 years.) Opportunity cost: $3,400 ($7K earning 8% for 5 years.)
Cost over lifetime average: $1500 per year.
It's important to note, also, when the brunt of the cost is born.
$17K car year 1 2 3 opp cost: 1400 1500 1700 deprec: 2600 2200 1800 ---- ---- ---- 4000 3700 3500
$7K car year 1 2 3 opp cost: 580 630 680 deprec: 1100 890 760 ---- ---- ---- 1700 1500 1400
So, if something major should happen after 3 years forcing you to sell the car, then the $7K car comes out even *more* ahead.