That modern m16/ar15 was designed in the 1950s and adopted around early 1963 the ar10 came later, but it's just a beefed up design around the larger cartridge. An akm (what most people picture in their head when you say ak47) was designed in the mid 1950s and began adoption by Russia in 1959 and other Warsaw pact counties starting around 1962 and 1963. They're almost identical in age. Ergonomics can be changed with a different safey selector, rails can be added with a different forearm, BHO can be had with the right mags, different stocks, etc can all be had, just like what is done with an AR. You can pick up an ak platform in a 16in 7.64x54r config and have a very close to ballistic equivalent to the 308.
ARs are cheaper to build right now, but that's just because so many people are in the game of making parts, etc in the US, it's supply and demand, when demand drops off from the record highs we have you'll actually see price points creep up. I know that seems counter-intuitive, usually when demand drops prices drop to lure customers in, but you'll see a lot of companies roll back production or leave the market entirely. Right now they're not making much per item but they're making good money with volume, when volume drops the can't afford to sell at the same profit margin. So I think long term wise that'll end up correcting itself.
AKs are cheaper to shoot right now, I see 1000 round cases of 7.62x39 and 5.45 in the $250-260 range, most places I see 5.56 in stock it's more like $275 for 500 rounds and cheap 308 is $380 for 500 rounds. Even in non panic buying mode and ak is generally cheaper to shoot. Getting into the AK game now it'll be more expensive than an AR, you're looking more $700-800 for a basic AK compared to $500-600 for a basic ar, but if you do any decent amount of shooting you'll start saving $ as you buy ammo.
It really just comes down to what platform you like and train with, either one is fine and has killed millions of people, they've both proved they're good in combat and both have had 60 years of combat staying power.