Registered automatic weapons are legal in most states.
That is true, but for 27 years, no new registerable automatic weapons have been manufactured. The registry is closed, and the number of machine guns transferrable to 'civilians' (non-LEO/mil) is fixed. That is why they are so expensive.
And every time they are transferred, the FedGov wants a bunch of fingerprints, forms, and $200. Every time. A buddy told me the average time these days is between 6 months and a year. Just to transfer a gun.
If Frankenfeinstein makes all 20 million or so AR-15's into the same class (registered with NFA, $200 transfer, fingerprints), how long will it take to transfer one of those?
Answer: you'll never get it. And she knows it.
RESIST, my friends.