Kermit the Frog was right: It's not easy being green.

Ever wonder what ever happened to the fun, funky alternative fuel vehicles that were promised in large numbers decades ago?

The problem often comes down to a different kind of green.

"It's a cost issue," says Bill Moore, publisher of EVWorld.com, a site devoted to electric vehicles and clean transportation. "In terms of technology, we've got it."

One company in India is trying to engineer a car that would run on compressed air, says Moore. It would have a fairly small range -- "about 60 to 100 miles" at a time, he says. "But it's one of the more interesting things out there."

NEVs or "neighborhood electric vehicles" (kind of like bigger, more passenger-friendly golf carts) can get you to the corner store and back. But since they have top speeds of 25 to 40 miles per hour, typically, they aren't allowed on some roads. And the range between charges is usually pretty limited, too.

But there are thousands of NEVs on the roads, and the number has been growing since 1999, says Brian Wynne, president of the Electric Drive Transportation Association, an industry group focusing on electric car technology. Still, he says, "it's not a big segment."

For a price, specialized companies will retrofit certain factory-made cars or trucks with a battery power source. And a few independent (and mechanically minded) folks have actually attempted the project themselves.

"Anybody can drive an electric car," says Moore. "You take the gasoline motor out and put in a battery."

But for the folks who like to buy cars in a more plug-and-play format, there isn't a lot to choose from when it comes to fossil-fuel alternatives. Still, a number of vehicles are grabbing some attention -- and ink -- lately. A few to consider:

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Chevrolet Equinox: Chevrolet began leasing a small number -- abut 100 -- of these four-seat crossovers with a hydrogen fuel cell power system last September. Expected range on a tank of hydrogen? About 200 miles, says Rob Peterson, spokesman for General Motors Corp. The lease will be available in Washington D.C., Los Angeles and New York, says Peterson. "From a performance standpoint, expect it to be equal to" similar gasoline vehicles, he says. Another unexpected plus: no oil changes.