What I found interesting was the TRD Griffon uses the JDM underpanels in conjunction with there custom panels and diffuser. The mid section would probably be cheap while the CF diffuser would be expensive. Mid section actually looks easy enough for any shop to fab. Only thing that worries me about the mid section is that the diff might overheat without the proper air.
My guess is the underpanels would help reduce drag and help smooth air out for the diffuser to actually create downforce
