You’re talking about EOTech optics. They run from $400-$600 bones. I have a Bushnell Red Dot/Green Dot on my AR, $242 including tax.
Not just those, but also Trijicon ACOG, and others, including one that looks like an EOTech but somewhat larger. Actually last I checked you could get the EOTech for about 325-350, unless you insist on night vision compatibility, but that's still mighty high for something for an AK, although not for an AR.