not sure, i was quoted £200 by LM audio sometime ago to fit the speakers build a sub enclosure and run the cables which wasn't too bad and fit the sound deadening, they would charge for the cables + deadening which I would have to buy anyway. i've done it before in my golf, not to the extent you have but only because i need the boot. I know running the power lead into the car is a pain on the golf and A3, you have to remove the glovebox to do it.
I might have a go at fitting it all asyou get a much better sense of acheivement, but I will definatly be happy if it comes out looking like yours