We're all about alternatives to gasoline here so when General Motors announced pricing earlier this week for the compressed natural gas conversion of its full-size 2011 Chevrolet Express and GMC Savana Cargo vans, we posted the info.

But the price did make us gulp – the base $25,980 vans become $41,890 vans after the conversions.

We know CNG is cheaper and cleaner than gas or diesel and we know fleet managers are looking for every way they can to cut a penny here and a penny there from operating costs (not to mention collecting green points from government, which sometimes extends benes to clean and green fleets such as preferential HOV lane access or a leg up in obtaining service contracts).

But $41,890 for a van?

So we called GM and got ahold of the Mikes – Mike McGarry, alternative fuels manager for fleet and commercial vehicles, and Mike Jones, fleet and commercial vehicles product manager.

They were worried that we somehow thought the vans were aimed at the retail market, but once we assured them that we knew the difference between a CNG-burning Honda Civic GX and a CNG-burning Chevy Express van, they relaxed and walked us through the financial rationale.

You've first got to understand that commercial vehicles have longer and harder lives than do most passenger cars and light trucks – 30,000 miles a year for 7-10 years isn't at all unheard of.

That gives the fleet manager more time to recoup up-front costs of alt-fuel or advanced-tech vehicles through accrued saving on fuel and maintenance.

It also helps to understand that in a fleet with loads of vehicles, even a penny a gallon saved on fuel costs adds up quickly to sometimes impressive annual sums.

The Mikes use a couple of assumptions in showing how the CNG conversion for their vans pays off – Jones said the difference in gasoline and CNG prices in many regions can result in a pay-back of the entire $15,910 in under 4 years.

Click here to read the rest of… How a $41,890 CNG Van Can Be Cheaper Than Its $25,980 Gasoline-Burning Cousin