Funny how the media immediately calls it an "assault" rifle.
Well, in this case, if it is a $50,000 gun and it is an M16, it's likely a Class III full auto, in which case it actually is an Assault Rifle in the actual definition.
Now, if he paid $50K for a semi-auto AR gun, then he is just completely stupid.
Transferable are running around $28-35k. Add some period correct items & a suppressor and you can get to ~$40k. There will be in-state sales tax too. There's a big NFA dealer down in Miami. Chances he got it from Mendiola.