I drive my personal vehicle for work all the time. You shouldn't get taxed on the milage. What it comes down to is what kinda gas mileage you get and what you're driving. I get 58 cents a mile and drive it on a 500 mile work trip about once a month. It's a beater civic I got for 5k and gets 30 mpg so it has just about paid for itself. If you're driving something newer or something with bad gas mileage, then I wouldnt. But if it's an old ford ranger or something, then it's kinda dumb not to.