I work 6 miles from where I live, and I drive a sensible car so it doesn't cost me very much... in fact, it's so insignificant I've never bothered to work it out.
A colleague of mine lives 60 miles from where we work, however, and not only does he have to pay his diesel costs, he also has to cross the Severn Bridge each day too.
Another guy I work with lives in Cardiff, which is 75 miles from where we work! However, he's a contractor and is easily earning enough to make it worth his while