I was hoping to see someone answer this question on the value of the piece you posted pictures of but so far have not see too much so I will take a stab at it. From what I can tell you, I had contacted a friend who has a stained glass store in California (40+ years) for another item of stained glass that a person wanted a value like you do for a certain stained glass panel they bought and it was from the late 1890's. Anyway, her response to that was: unless you know who the glass artist is that made the piece and they are well known, then a value can be put on the item from the artist's known works, but, if the artist is unknown and you cannot identify a certain artists' works, then the item is valued at whatever a person will pay for it. I know that does not help you to determine the value of the item, but that is what I have been told. I also do know that there are people who can tell if the gems used in the stained glass item are old (100 years or so) or if they are newly made, but I do not know how that is done, nor do I know who can or how to tell the difference in the gems.