Congressional Budget Office Cost Estimate: Estimated Budgetary Effects of H.R. 7910, the Protecting Our Kids Act [open pdf - 168KB]
From the Document: "H.R. 7910 would change federal gun laws by creating new federal crimes and expanding federal firearms regulations. Specifically, the bill would:  Raise the purchasing age for semiautomatic rifles from 18 to 21;  Ban the import, sale, manufacture, transfer, and possession of large-capacity ammunition feeding devices;  Establish new federal crimes for gun trafficking and straw purchases;  Require gun owners to meet residential gun storage requirements and establish criminal penalties for violating those requirements;  Require registration of existing bump-stock-type devices under the National Firearms Act and bar the manufacture, sale, or possession of new bump-stock-type devices for civilian use; and  Change the definition of 'ghost gun' and require background checks on all firearm sales[.]"
Congressional Budget Office: https://www.cbo.gov/