Well, if you know where the affordable assault rifles are, please tell me and we'll split the profits!
Assault rifles are the lowest powered rifles the American military has ever used since the development of the brass cartridge. When introduced they were dismissed as squirrel or poodle guns. Many states don't allow them for deer hunting because they're not deadly enough for a clean kill.
All rifles combined, not just assault rifles, are virtually irrelevant in homicide statistics, and many of those used are by drug cartels (sometimes armed by the branch of the federal government charged with enforcing gun laws). More people are murdered with clubs and hammers than rifles, and about twice as many are killed with bare hands. About four times as many are murdered with sharp pointing things, and five times as many are killed with "other weapons" (probably frozen turkeys). More people are also murdered with shotguns than all rifle types combined
Since the assault weapon ban expired
, the murder rate has dropped by about half. So at best, in a magical world where a rifle never killed another person, the murder rate would drop to 98% of the current value. In reality, it might jump back to 200% of the present rate, because that's where it was during the last data point we had for an assault weapons ban. Yet re-instituting the ban would probably prove irrelevant to murder rates because assault rifles are so irrelevant that the FBI doesn't even bother breaking them out into their own category. The US murder with assault rifles is probably around 0.03 per 100,000. They're not even common in mass murders.
You could instead go after the deadly threat presented by legally owned fully automatic FFL weapons. A lot of my friends own those. Heck, even I have belt fed Browning. Yet the murders committed with those is listed as just 2. Not 2 per 100,000. Not 2 per year. Just two - in the entire database.
In fact, given the overwhelming popularity of assault rifles and their virtual non-use in homicides, it would make more sense to trade everyone a brand new assault rifle for every piece of rusting junk they drag in, like old revolvers, knives, hammers, and frozen turkeys.