It costs nothing to put bans and controls in place because already have departments/resources that are doing it
Unfortunately that simply isn't true. Want to ban something? Paperwork has to be filled out; legal documents of all sorts need to be modified (if only to include the line ", and magazines of capacity greater than 7"). All that paper work takes time of government employees, those employees cost money.
And, since you can't make something happen by simply including a new line in a legal document, you need to educate people (that may be as simple as sending out notices to all affected manufacturers, middle-men, and retail sellers), and you need to enforce it (and that means sending out personnel to speak with and inspect all of the above). Again, more time.
Yes all these resources are already employed by the government, but those people are already doing work (one hopes), this is new work, and has to be accounted for as such.
Going slightly deeper, the increased demand on back-ground checks will require additional resources to handle.
I haven't read the details of the package, and since, as a Canadian, it doesn't directly affect me, I probably won't. But one thing I won't do is underestimate how much work it takes to change the course of a massive industry, such as the US firearms industry, even just a tiny bit.