How much is this painting worth?

If you're sure it's an original work rather than a print of some kind, it may be useful to take it to one of the big art auctioneers. There was a British artist by the name of Norah Pearse, with many of her works passing through various auction houses. The dealer is fairly irrelevant unless they were also the agent for an artist. If you had posted up a link to a photo of the actual work, we could have compared it with Norah's.