General Motors has released pricing for Bi-fuel option for the Chevrolet Silverado and GMC Sierra 2500 HD 2500 HD, and it is a pill that probably will not go down easily. Buyers who want their horses to work sucking down either compressed natural gas (CNG) or gasoline can look forward to ponying up to $ 11,000 for the pleasure. That big chunk of change adds a Type 3 tank bed for CNG, and GM says that with both fuels, the trucks will have effective range of 650 miles. The bi-fuel option is available on any heavy-duty truck configuration, including four-wheel drive and extended cab models.