If you’re going gas of whatever type, cast iron grates are good. They’re not as important with charcoal because that gets hotter. Anecdotally, I’d say those make the most difference in a low end gas grill than without.
When you look at the price of cast iron grates alone, it’s like $80-100+. hose are plain iron. Even if they’re pre-seasoned, you have to oil them all the time till you build up a good film. (It’s pretty easy, but easier not to.) If you don’t, and live where there’s humidity and water, they’ll rust like crazy during the non grilling period.
I don’t get thick cast stainless steel grates. Stainless has much worse conductivity than cast iron.
This may help-