The replacement discs are £292.45 each so £584.90, if it were me i would offer the seller £550 and see what he/she says, it depends what pads are in them i suppose as if the pads are crap you will be looking at another £250, if the pads are a good brand and good life in them you in for a good deal
you discs and calipers would probably be £250?, again pads would alter the price depending on whats in them