Some things are expensive and some are cheap.
Cold beet (red beet) soup with baked potatoes - it's called kholodnik (or cold borsch), potato pancakes.
You will find plenty of chicken dishes and mostly freshwater fish.
You also have vegetables, mushrooms and fruit.
I found prices very reasonable as an American. I can't compare to Poland as I have never been.Edited: 10 August 2018, 19:47