Do you plan on doing much range shooting? If you want to shoot the weapon often the AR-15 will be more accurate, less recoil, and IMO more fun. If you want to have a rifle just for self defense or shtf scenario I would go with the AK-74 as it has more punch and can take a lot more abuse. As these are the two most popular rifles in the world, availability/cost of ammo will be a wash in the long run.
Either way you might want to wait a couple of months as I don’t think congress or the tyrant in cheif can act that fast and I see prices going down slightly.
I would certainly use it at the range but not a lot. It’d mostly be for defense, or offense if comes to that.
What are you talking about? The two rifles are within a few thousandths of an inch of being the same caliber! You are thinking of the AK-47 in 7.62, not the '74 in 5.45.