I got a quote last week on a Corbin seat for my 750ss and it was £280. I think it was from Equinox.
Another option you could look at is the Sargent seat.
http://www.sargentcycle.co.uk The quote I got on that one was £275 from Calamander.
I colleague of mine has a 900ss with the Sargent seat and is really very happy with it. And it also looks the business! Same person is also quite short and has had the ride height on his bike lowered.