All three windows stopping working sounds unlikely, more than likely all four window don't work, or is an intermitant problem, to my my knowledge, the window use only one relay and fuse, so ruling that out any faulty electric window regulator, motor window switch etc... Can easily be repaired by a auto electrican or can be fixed by your self sorcing used parts at wreckers etc, $1000 Is cheap for a 114000miles 325i and as long as there is no rust, I'd buy it!!