The Ferrari ownership cost report that Travis found told us that a 1993 Ferrari 348TS cost about $2.57 per mile to operate, if you leave depreciation out of the equation. That's not great, but it's far from the costliest vehicle to operate.
Considering that the Ferrari included over nine grand in scheduled maintenance, there are obviously cheaper ways to get around. Then again, a twenty-year-old 348 is hardly top-tech— the bill for sending a probe to Mars probably eclipses that many times over. What about a rocket? A 747?
What's the most expensive vehicle (plane, boat, houseboat) to operate per-mile? Just to make it fair, as the costs are obviously dependent on distance, try to keep it close to how far it would go in a typical year of use.