For example, the price of the fish was stated as 2.40 rubles. This is meaningless outside the context and does not explain why it was very expensive for the old man who checked the fish first. But if one knows that this was Soviet SF that was about a life in a small Soviet town of that time, then one also knows that a monthly pension was like 70-80 rubles so the fish cost was a daily income.
Then one needs to remember that the only payment method was cash and people did not go out with amount more than they would expect to spend to minimize the loss in case of thievery etc. and banking was non-existing in practice so people hold the savings in cash at home. That explains why Lozhkin went to home for the money.