Building on Picher's handloading observation, the reason I acquired a couple of non-autoloading rifles in .300 AAC/Blackout was the very broad range of handloading possibilities:
In a pinch, you can make brass from once-fired military 5.56
You can use either small pistol or rifle primers (with proper care!)
You can use jacketed .312" pistol or rifle bullets (I bought a .309" Lee bullet sizer for this)
You can use plated bullets
You can use cast bullets
You can use a wide range of pistol, rifle and shotgun propellants
There are other rifle and cartridge combinations that permit most of these possibilities, but not necessarily all. For example, large rifle and pistol primers are not dimensionally swappable. The .308" bore offers about the widest bullet availability, and the .300 AAC was intended to work with both heavy and light bullets. It is fairly thrifty with regard to lead and propellent use per round.
My point isn't so much that .300 AAC is the absolute cheapest way to shoot at all times and every circumstance. However, it may be the cartridge you can most readily handload in times of scarcity, when components for some other cartridges are unavailable. And there are/were some fairly inexpensive bolt action and single shot rifles available for it. I went both ways, with an AAC-branded H&R and a tricked out CZ 527: