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I am not sure of the answer to your question ... but, as far as I know, it is an add-on cost option for the aero kit. Even for the M45 Sport.
EDIT: Yes, I just checked. At the Infiniti web site http://www.infiniti.com
, if you configure a car for purchase, even the M45 Sport has an option for US$1390 to add the following item (this is in the US market ... I do not know what Canadian Infiniti dealers have to offer):
"Aerodynamic Body Kit
Aerodynamic body kit includes front and rear lower fascias, side sills and rear decklid spoiler."