With dedication by name I would say £500-600 inclusive based on last's year results. It's a lovely pic, though, so I would add more for that, 1 or 200. Presuming it's authentic.
Unfotunately its between £1000-£1500 which I believe is too much for such a piece which is why I asked what other people thought it was worth. I am sure it will sell though at auction over here but it is a lot of £££££s.