I'm doing about 70-80 miles a day, 5 days a week and have been for the last three years and have just hit 105k on the odometer. When I fill up these days I very rarely pay any attention to the cost, otherwise I think I might think twice. Trouble is, I love the car too much to get rid... well that and new cars cost a (not so) small fortune these days.
By driving carefully (or like a boring old fart, take your pick) I can usually manage about 350-400 miles from a tank, which means that I can "get by" only filling up once a week...