Randy, yes, it's just a one time $200 tax stamp fee. You will also have to fill out a bunch of paperwork/finger prints. As others stated in your previous question if it has a 10.5 inch barrel and you add a pistol brace it's just considered a pistol and no tax stamp necessary. Now if you add a shoulder stock to a firearm with a barrel less than 16 inches it's considered a SBR/short barreled rifle and requires the $200 tax stamp. Right now the atf is trying to change the meaning of what a stock is to include pistol braces though. If that isn't overturned then even ARs with a barrel less than 16 inches that have a pistol brace will be considered a SBR but if you already own one with a pistol brace they're giving out free one time tax stamps. Hope this helps.

Randy, yes Sir, it is a one time fee for each registered NFA device or firearm such as an SBR or a Suppressor. Cheers and stay safe!