James Roosevelt Daguerreotype Value?

My dad has a Daguerreotype of the great grandfather of Franklin Roosevelt, James Roosevelt. It is the only one in existence. James is also distantly related to three other presidents - Theodore Roosevelt, Zachary Taylor, and Martin Van Buren. The Daguerreotype was taken in 1840, 7 years before James's death (he lived 1760-1840). The Daguerreotype also has a handwritten note from James Roosevelt Jr., son of FDR and United States Congressman himself.

We have no intention of selling it but how much do you think it would be worth? I would say the condition is fairly good and it is about 4.5 X 3.75 inches.

Here's a photo of the inside (it's sort of formed like a one page book with cardboard like boarders/covers). The spots you see on the inside are just from the reflections of the many mirrors, there aren't actually many spots:

<embed src="https://www.box.com/embed/1vmt2k91gl2ct3t.swf%22 width="466" height="400" wmode="opaque" type="application/x-shockwave-flash" allowFullScreen="true" allowScriptAccess="always">

And if you're curious, here's a link to James Roosevelt's wikipedia page (notice the lack of a picture):

http://en.wikipedia.org/wiki/James_Roosevelt_(1760...

So again, approximate value? Thanks!