Welcome the site, can't give you much info. other than Durs Egg guns in their original flint-lock form can be quite expensive, percussion not so much but it depends on the gun and desirability.

Years ago I picked up a Durs Egg SxS, well actually all but the stock. It has been converted from flint to percussion greatly lowering the value of even the parts.

Some more knowledgeable might chime in.--- John