Gas Prices in Perspective , an article I found while looking for information on the automobile depreciation from vehicle miles traveled. It addresses the issue of working hard to save pennies on gas but paying for convenience at a Walgreens/CVS/etc. The OmniNerd website deserves a look.
How much does mileage contribute to automobile depreciation? It is an important item in the discussion of fixed vs. variable costs of owning a car.