Suppose that the U.S. repealed the Second Amendment and banned all firearms ownership. This would still be a "taking" and the government would have to compensate gun owners for their property.
There are about 300 million guns in private ownership in the United States. Suppose that an average gun in private ownership is worth $1,000. So this would cost about $300 billion.
$300 billion is not chump change, but it is also less than half of the budget of the Department of Defense for a single year. And, while many of the confiscated guns would be destroyed, some could be distributed for use by law enforcement and the military, both in the United States, and among our allies (e.g. the Afghan government might appreciation receiving some at a favorable price). The use of firearms for game control would be limited to trained park rangers who might also get some of the guns.
If those guns could be removed from the streets, the savings in reduced accidental deaths, suicides, and homicides in the U.S., and in other countries to which guns from the U.S. are smuggled (mostly in Latin America) would make that expense worth it in short order.
Admittedly, a national gun confiscation scheme, a gun rights activist's worst nightmare, wouldn't be perfect. Some people who are otherwise law abiding, and some people who are not law abiding, would retain some of those guns, and other people would covertly manufacture new guns on a small scale. But, even if only 90% of guns were successfully collected, that would lead to a large share of the benefits being accrued.