Of course synthetics are cheapest, but they don’t last very long, and you still have to pay a pretty penny if you want optimal styling (and maybe add highlights as well). But it’s definitely the most kosher option.
One of the ways to cut costs on human-hair wigs is to buy shorter ones. And there’s a major tznius bonus to boot. Length is a major part of wigs’ prohibitive cost. Hair doesn’t grow all that fast if you’re talking feet, not inches.