Where did you get the $5 info, just curious? Transfer to lawful heir goes on a Form 5 - "Aplication for Tax Exempt Transfer and Registration of Firearm"
http://www.atf.gov/forms/pdfs/f53205.pdf
The form 5 needs a sign-off and fingerprints so there would be the expense for that.
I stand corrected. I have not nor do I see in the future inheriting any NFA. Anyone want to include me in their will just to piss off your family? Guess I was thinking of a AOW