Hit!

Did you guys see the stats/numbers?

In other words, the number of bump-stock-type devices held by the public could range from about 280,000 to about 520,000.
Since the majority of bump-stock-type devices are made of plastic material, individuals wishing to destroy the devices themselves could simply use a hammer to break apart the devices and throw the pieces away.
Overall, ATF estimates that the total cost of this proposed rule would be $297.2 million over a 10-year period of future analysis.
They don't clearly separate out the government vs private costs. But assuming all private costs are incurred in 2018 from destruction and surrender, this rule change is going to cost taxpayers about $20M each year.

Imagine what a mag ban would cost!

Oh, and if these were metal the destruction costs would be greater which would make the rule change appear to be more expensive. Their assumed costs are based on individuals being able to take a hammer to break them apart.