TTN, a 130 m long yacht is roughly twice as long as an A330-300, and if we assume the beam and overall height are twice as much too (a very crude estimate I know), then we are talking four times the surface area. Also the yacht has complex exterior features and as you say yourself would be labour intensive to paint. So if 1m€ is ok for the yacht, then £900k seems a tad expensive for the aircraft.