The permits are no expensive ,it requires experience in order to obtain the US Fish and Wildlife liscense to mount migratory Birds FOR THE PUBLIC, if you are doing it as a hobby for yourself or friends without charging you don't need a permit.
You can go to the public library and check many waterfowl pics and choose how you want the duck mounted.

I charge $165 for small ducks
$200 for Medium ducks
$300 Large ducks On driftwood , scenery with plants and bases is extra.

A good duck mount is 8 to 9 hours of labor, so don't think the taxidermist is making a killing at those prices he'll be lucky if he clears $8 an Hour, a taxidermist should make $50 an hour ,but if he charged that a duck would cost $400 to $500.