In my school in Moscow during the Soviet days, we had two types of lunches. "Student lunch" cost 28 kopeks. You could also buy supposedly much better "teacher lunch", which cost 32 kopeks. I don't recall much difference, other than the portion being a bit larger in the case of the latter.
Typical menu was some kind of soup (schi or borsch) with sour crear and grease floating in it. Rye bread was also available. Then "kotleta" made out of mystery meat with a spoonful or two of mashed potato. And then "kompot", a fruit drink. Not terribly tasty (except for kompot:). And probably not very healthy, either.