They fetch at least £500 a set with discs( maybe even pads too, never looked though)
Alex is your best bet though as others said, you know you're not going to get a set with seized pistons etc.
having only driven 2 zeds with normal brakes(old zed has totally standard brakes, this zed has some sort of uprated discs, pads & lines) I can't say how much, if any, brembo's are over the standards