Quick and easy, all paint matched body color (because of your white wheels)...
Greddy "Gracer" front lip for BR-Z
Chargespeed side skirts & rear spats (real or knock off)
http://www.ft86club.com/forums/showthread.php?t=31433
OEM "style" rear diffuser
Anyplace for $50
Make sure to paint match otherwise it will look garish.