Theres one for sale in a bike shop over here, 1 of only 2 or 3 in the country. I think it's being sold on behalf of owner rather than being shop stock.
It's listed as P.O.A but given how other models have sold I would think it would go for somewhere in the $25,000-$30,000NZ price range, about 8,000-10,000 sterling. Purely because of it's rarity here.
There is a Strada for sale privately as well which has $19,000NZ as the asking price, about 6500 sterling. I think it's a bit overpriced as they normally command about $15,000NZ, 5000 sterling for a good one.
851's fetch 3500 - 4250 sterling. There is quite a few more of them around.
My bike is the only bike of all these models I ever see on the road though, all the others must just sit in the garage.