these have been going a LITTLE nut over on Ebay and other
but my point is list it there
you go to that item and then at the left side and look for complete listing and you will see what has the pricing in green sales
you need to know something about the pistol to which model it in the time line and if it has extra front sight inserts the screw and plate for the sledge clamping which grip it has, sports or target, things like that
here are some pictures at the Vintage
https://forum.vintageairgunsgallery.com/feinwerkbau-pistols/feinwerkbau-modell-65/
message me if you like
good luck
mike
normal pricing would 500.00 to 700.00 but condition is a factor and if the seal and buffer have been replaced