Total Parts Cost w/Shipping was $155 USD. Once I have time to install it, I may not need all of the parts I have shown. These parts were selected by Subaru as an assembly. So say you needed to replace the entire rear bumper and its accessories, you would need all of these parts. However, just replacing the plastic piece on our USDM may not require all items shown.
If I have to, I will find a similar connector to this rear fog plug that will allow me to pin my own connector and run the wire to the relay for the front fog light options which I will not use. The front fog light relay and wires should be there since its a dealer option. If that is the case I will simply buy the stalk for the USDM front fog light operation and simply tie it to the rear instead. This way it gives a clean factory look and operation. Otherwise you can simply add your own switch on the column or dash as you see fit.
I went by the local dealer who has a STI on the showroom, got underneath and checked the backside of the plastic panel. From what I can tell is it has clips on both sides that hold it in place. It is a separate piece from the rest of the rear diffuser so it can be removed and replaced with the rear fog. However, until mine comes in and I can take the bumper off to get a clear view of what is back there to mount, I do not know how plug and play the light is.