(b) Except to the extent that a passenger car rental described in subdivision (a) of this section, or section eleven hundred sixty-six-b of this article, has already been or will be subject to the tax imposed under such subdivision or section and except as otherwise exempted under this article, there is hereby imposed on every person and there shall be paid a use tax for the use within the metropolitan commuter transportation district as defined in subsection (a) of section eight hundred of this chapter; of any passenger car rented by the user that is a purchase at retail of such passenger car, but not including any lease of a passenger car to which subdivision (i) of section eleven hundred eleven of this chapter applies. For purposes of this subdivision, the tax shall be at the rate of six percent of the consideration given or contracted to be given for such property, or for the use of such property, including any charges for shipping or delivery as described in paragraph three of subdivision (b) of section eleven hundred one of this chapter, but excluding any credit for tangible personal property accepted in part payment and intended for resale.