The full kit is £240 + shipping (Only found this kit on one website and not really looked anywhere else yet).
+shipping, having the sh*tty fiberglass fabricated to make it stronger and more durable, fitting, Painting of the entire rear bumper I'd say the total cost would be nearing towards £400.
However I'd then have the front bumper and skirts which I can sell on-
The exhaust system I've been quoted on is £550 which includes a sports car, and full stainless system from there back, including dual exit pipes (Proper ones!), with whatever tailpipes I choose.
Yes it's a lot of money, but with the engine plans I have for the car- I'm never going to make my money back on it anyway, so planning to keep her as long as I possibly can.
AND- I'm able to do it in doses. TBH I don't think the rear of the car pictured looks too bad with only 1 backbox. Obviously it'd look better with one either side, but what I mean is- I could get this rear valance, and fitted, then a few months down the line when it suits me- Have the exhaust system fitted.