I'm looking at adding a 300 AAC blackout to my .223 since I can change out the upper and I'm good to go. Would also like to add 10mm, probably in a Glock. Sorry. Maybe a .45acp but I already own a 45LC but I feel the need to get a 1911. But finances get in my way as I'm retired so I have to watch not only the price of the gun but the price of the ammo.
Over my firearms hobby, I've supported the following cartridges:
.22lr
.22WMR
.380 Auto
9mm
.38 Special
.38 Special +P
.357 Magnum
.45 Colt
.45 ACP
.40 S&W
10mm Auto
5.56 NATO / .223 Rem
.308 Win
7.62 x 54r
7.62 x 39
12 gauge
.410
Fraction the ammo budget between all of those, and it was difficult to build up a stock of ammo as a buffer against supply/demand/price fluctuations. The amount of firearms that just sat in the safe got ridiculous.
Today, both the number of cartridges I support and the number of firearms I own is much less. I'm more than comfortable with the ammo I have on hand.