Undertray is $204 shipped from TBW on ebay. Great buy, comes with hardware. I have one and it really helped keep my stillen fascia from flexing. The two pieces of the tray do not line up well in the middle however, be prepared to jury rig to make it work if you have an aftermarket front bumper.
Aluminum Engine Splash Shield Under Tray Cover for Infiniti G37 Q60 Nissan 370Z | eBay