St. Petersburg - Lunch while on Tour

I have scheduled a Denrus tour off of a cruise in August and am wondering if anyone has any advise as to what lunch option they have experienced? Given the makeup of our group we have opted out of the lunch with a Russian family. But Denrus is suggesting some restaurants and the meals seem a lot more extensive and heavy than what I ordinarily eat in the middle of the day. As well as at least twice as expensive ($15 - $25) I am sure I can tell them that I want something simpler but am looking for tales of what others have tried and liked.