Here's an article in 2004 about a $2000 gizmo (not counting installation cost) for home natural gas fueling in the U.S.:
http://www.msnbc.msn.com/id/5960905
As mentioned:
Honda said the unit offers a "personalized solution" to the fact that natural gas is not sold at gasoline stations.
"The biggest obstacle to broader acceptance of natural gas vehicles is the limited availability of refueling stations," American Honda Vice President Tom Elliott, said in a statement.
Also, it takes about six hours to refuel with this gadget, so has similar problems to electric vehicles. Assuming it did become popular, there would need to be massive upgrade of the infrastructure to handle the added capacity, and vehicles to use it. Compare that to the FFVs already on the road, and the relative ease of increasing them and use of methanol.