I paid ?260, but that was before brexit.
The cheapest I can find right now is ?299.18 https://bmw.europe-moto.com/gb/seats-moto-bmw-motorrad/9860-bmw-driver-seat-m-sport-high-hp-s1000rr-k67.html, it says VAT included but you may be rolling the dice when it comes to import fees.