You missed the AK-74 bus by a few years. Milsurp 74 mags usually run $25+ now. They used to cost anywhere from $3.99-10 depending on if you bought EG bakelites, surplus Bulgarian, or "surplus" Bulgarian like the firebrick and tan mags. After market US and Bulgarian mags exist from $10-15 dollars but I believe they all lack metal locking lugs.
47 mags can still be had at a great price. Polish, Romanian, and other former combloc mags are regularly available for $10. The exotic stuff like waffle mags, bakelites, etc... start at around $40.
Ammo availability is pretty much the same and so is the price with 5.45 usually being slightly more expensive. From a rifle availability stand point there is alot fewer 5.45 options you have either Arsenal, kit builds, or older Romanian Sar-2s. This makes 5.45 guns a bit more expensive. For 7.62 rifles you have new wasrs, Arsenal, and various us made options like PSA, Atlantic Arms (kit builds), and Riley. All have decent-good reputations and the variety of manufacturers make the price range of a 7.62 gun more attractive at $500-$1200 vs $800-1200 for a 5.45 rifle.
Avoid Interordinance I/O and century's US made guns at all costs. They both show a problematic trend of very early wear and critical component failure.