What costs less? The $26,000 Nissan Leaf or the $24,000 Chevy Impala?

The Leaf actually runs about $17,000 less, when you include the total fuel costs over a 10-year period, estimate that gas will cost $3.61 a gallon and include the $7,500 federal tax credit for all-electric cars, according to a cost calculator created by the Rocky Mountain Institute.

Over the 10-year period, the Leaf will cost its owner $25,680 while the Impala will run $42,680.

The calculator, part of RMI's "Project Get Ready" initiative to acclimate policy makers, consumers and manufacturers to the coming changes to transportation, exists to provide somewhat close and realistic cost estimates for hybrids, plug-in hybrids and all-electrics, according to Tripp Hyde, the RMI analyst who came up with the application. (Note: we called it People Get Ready at first, which was a Curtis Mayfield song.)

Cars with large batteries simply cost more than their gas counterparts because batteries cost a lot. Lithium-ion battery packs for all-electrics right now cost about $900 to $1,000 a kilowatt/hour and all-electrics like the Leaf need about a 25-kilowatt/hour battery. The plug-in hybrid Chevy Volt coming from General Motors will have a 16-kilowatt/hour battery.

While car makers and battery manufacturers want to drop the price to $500 or $300 a kilowatt/hour in the next several years, that's still a lot of extra cost.

Consumers, thus, need to understand how batteries can cut their total costs because of lower maintenance and lower fuel prices.

If anything, the application has variety, and lets you compare the Tesla Roadster and a Dodge Ram truck (The Dodge is still cheaper in most cases – you need to drive 38,000 miles a year for 10 years on $5 a gallon gas to get the Tesla to cost less.) or a regular $22,000 Toyota Prius with a $49,000 Toyota Plug-in Prius (Regular Prius cheaper after 10 years with $4 gas – $39,000 to 49,000).

The $40,000 Chevy Volt or the $22,000 Jetta Diesel? After 10 years, the Jetta still rules, $34,000 to $41,000. It's great fun. Click here.

The calculator does make some assumptions. The federal tax credit is baked into the estimates for all-electric cars, but it can be eliminated from the calculations. (Europeans using the system, for instance, need to eliminate that and calculate by hand their own benefits, which can be far higher.)

The system also uses a price of 9 cents per kilowatt/hour for power, the U.S. average two years ago when work began, Hyde said. It will likely be revised to 11 cents a kilowatt/hour which is now closer to the U.S. average.

The calculator does not include estimates for replacing the battery. But by 2012, batteries for electric cars should be capable of driving cars 100,000 miles, so replacement costs will be less of a factor in buying decisions.