This comes under the heading of 'no-brainer'. For long trips, I always rent a car rather than drive my own. I enjoy driving a late-model car with better appointments than my beater, but what I most enjoy is saving money.
How much, you may wonder, do I save? On a hypothetical week long trip from my home in Central Ohio to Daytona Beach, Fl and back, I calculate I'd save almost $500. How?
At the moment, a mid-May, Saturday to Saturday rental of a compact such as Nissan Versa from Enterprise would run me $202.81, tax included. I never buy their insurance coverage, as rentals are covered by my personal auto insurance, and the $500 deductable won't break me. I've been renting cars for years, and had I paid for this coverage each time, I'd have given away thousands of dollars.
Currently, the IRS deduction for mileage is $.485, and this number not picked out of the air. The largest part of it is based on the average depreciation and maintenance cost of an auto. Commute Solutions has a worksheet to calculate the true cost of driving, which uses the figures of $.286 per mile for depreciation and $.059 for maintenance.
If my trip is 1,988 miles ( there and back and 10% for around-town driving), and figuring the cost of gas is a wash between the rental and my usual ride, the depreciation and maintenance I save on my own car comes to $685.66. Even after paying for the rental, I end up saving $483.05.
Peak travel periods can skew this, as car rental places raise rates. Nonetheless, it's not hard to save some serious cash by driving a rental. Enough to pay for a really cool rental, if that's your style.