The Gupta empire was made up of
Brahims a.k.a the priests
Vaishyas a.k.a merchants and tradesman
Shudras a.k.a Peasants
Kshatriyas a.k.a warrior and rulers
The fourth choice satisfies this list.
Although opportunity cost is definitely important, it is hard to put a "price" on the opportunity in many cases, which makes it unmeasurable. This is why economists focus almost exclusively on price.
