Demonstration Vehicles under 42 U.S.C. § 6374(d) says that when purchasing alternative fuel vehicles for demonstration purposes, agencies will not exceed the cost to off a comparable gasoline- or diesel-fueled vehicle for half of the demonstration vehicles.
(d) Federal agency use of demonstration vehicles—
(1) Upon the request of the head of any agency of the Federal Government, the Secretary shall ensure that such Federal agency be provided with vehicles acquired under subsection (a) of this section to the maximum extent practicable.
(A) Funds appropriated under this section for the acquisition of vehicles under subsection (a) of this section shall be applicable only to the portion of the cost of vehicles acquired under subsection (a) of this section which exceeds the cost of comparable gasoline or diesel-fueled vehicles.
(B) To the extent that appropriations are available for such purposes, the Secretary shall ensure that the cost to any Federal agency receiving a vehicle under paragraph (1) shall not exceed the cost to such agency of a comparable gasoline or diesel-fueled vehicle.
(3) Only one half of the vehicles acquired under this section by an agency of the Federal Government shall be counted against any limitation under law, Executive Order, or executive or agency policy on the number of vehicles which may be acquired by such agency.
(4) Any Federal agency receiving a vehicle under paragraph (1) shall cooperate with studies undertaken by the Secretary under subsection (b) of this section.