I am from the bike industry, I can help. In the old days there were different hardnesses of metal in cogs. (Rockwell hardness test) an old Regina had teeth that were soft, Rockwell hardness test of 20. A Suntour would have hardness of 40, very hard, like a file. All of the Shimano cogs are a hardness of 30 except Dura Ace which had a few Titanum cogs, but otherwise 30 hard. The less expensive cogs are typically no finish (black) bump up the price and you get galvanized cogs. bump it up a little more and you have something they used to call Cromica (or something like that) next up is low grade chrome,. Next grade up and it's buffed chrome. So all the higher cost is largely about the aesthetics. As you pay more, the holes get a little bit bigger and on the chrome cogs, some have an aluminum center, for lightness.
I have had really good luck/ super nice shifting from Sunshine cassettes, Not as nice shifting (sometimes) with the low end SRAM casettes. You can't go wrong with the Shimano cassettes.