Two years ago a big duck (mallard, can, etc.) was about $275 at an established place. I think he said the price was changing to $300. I know another was done at a smaller shop/private guy and that cost about $225.
Good luck, that should give you idea to start at anyway. These were for flying and sort of banked to show both the breast from the bottom but also the color on wings, like they are turning right in front of you, with a simple driftwood piece behind it.
-Box