This is Part 3 of a 5-part back-and-forth between my friend Jason and myself as we compare the eco-friendliness of the Kia Soul and the Toyota Prius.

Yesterday, Matt's comment brought up a point I wasn't sure if I wanted to touch on this week. Specifically, total energy costs/mile comparison figures. It's a good argument. It's an important argument. It's just not the one I was planning to make.

This argument (see pgs. 10-11) points out that in terms of total energy costs over the life of a vehicle, the Hummer H3 costs 1.95 cents/mile. The Toyota Prius? 3.25 cents/mile. (Note: the overall winner is the Scion xB at 0.48 cents/mile) How can this be?

These figures take into account the energy necessary to plan, build, sell, drive and dispose a vehicle from concept to scrappage. It's an even more expanded version of how Jason got us to think past only a vehicle's "miles-per-gallon" impact yesterday. And hybrids currently add the significant drilling and energy costs of manufacturing, replacing and disposing additional batteries, electric motors and more complex power packages.

The reason I didn't want to make this the crux of my argument is because I can see this getting better over time as technology improves (hybrids are relatively new). And in a perfect system where companies are charged accurately for their third-party pollution costs when mining, these costs would be reflected in the cost of the vehicle production and therefore, the vehicle purchase price. Plus, with global oil production staying stagnant and oil demand increasing exponentially (China/India), higher oil costs in the future may help even out these numbers.

So, here's my argument. All things being equal, if your true goal when purchasing the Toyota Prius is eco-friendliness, is this the greatest use of your dollars? For instance, most studies show that it takes 15 years to make up the premium cost of the hybrid with your savings on gas. So, from a strict personal economic analysis, it's break-even at best.