At one time, they were allowed on ebay.

It depends if the badge is full sized or a courtesy mini badge.
If its a mini badge about 1- 1 1/2 inches in size about $10-30.
Full size quite a bit more.

Many N.Y.C. Police officers had these mini badges made up with their shield number on them.
They would be given to friends or family as a keepsake. Primarily if you were ever stopped for a vehicular violation in N.Y., you would hope that by presenting this you might avoid getting a summons