The federal reimbursement rate is 53.5 cents per mile. I've seen some studies that put the cost of car ownership at over a dollar per mile, taking into account gas, devaluation, fees, insurance, maintenance, etc. The cost of a car is astounding.
Also, last I saw, the average length of car ownership in the U.S. is 4.5 years, so take your 20 year estimate, then cut it in half, then cut it on half again.