Aziz, those prices are from the final days of Francotte's existence - note the date at the bottom of the web page you reference is '10/11/96'. The company was near death several times between 1959 and 1989; looks like this time it's for good, though.
I suspect MickeyD is pretty close w/ the 2nd part of his estimate:
well over $10,000, maybe double that
If you'll answer the questions in my earlier post, which include a request for more pics, I'll give you my 1 cent worth.
BTW, if it were anything other than a 12 ga, it would be even more valuable.