BIG DEMAND: Money back guarantee: Let's say years later you want to sale your Nat/gas set of wheels.
There are several dealers that specialize in NGVs & other alt fuel vehicles, and there are always a few listings on the "bay". Honda Civics, Ford Crown Vics & Chevy Cavaliers are some of the more common ones, also quite a few pick-ups. They carry a pretty hefty premium. On a 10-12 year old car you can probably expect to pay at least $1000-$2000 more than a gasoline or diesel powered equivalent. For example: an '04 Chevy Cavalier BI-Fuel, over 110,000 miles, sold for $5300. Not sure I'd pay that much for that car,(its a 9 year old CAVALIER) but I see it as a positive sign. JMO