I also did some searching too, and the brand of caviar they're eating in this chapter is actually a real brand, and it costs almost 23,000 yen for a small jar of 25 grams.
Although the real thing comes in jars instead of tins, I looked at similar-sized tins that were around 30 grams.
The highest number of tins that can be seen in a single panel is 7, that would make the total cost of the caviar they ate at least 159,138 yen (or 1,056 USD/978 EUR).