The large amount of each individual's expenditure could be tallied together as a single large amount of money, but the pluralization expresses a sense of the complexity. Even the large amount of an individual's expenditure can be expressed as a plural to communicate the various budget items or transactions within the expenditure:
Amount: a quantity of something, typically the total of a thing or things in number, size, value, or extent. But for amount the second meaning given is " a sum of money ", EX: They have spent a colossal amount rebuilding the stadium. Amount can also be a verb, unlike quantity, and it's the following:
This is confusing because both 'amount' is a mass noun and 'data' is naturally taken to be a mass noun but pedantically is considered the plural of a count noun (with the rare 'datum' as the singular).
word choice - When to use "amount" vs "amounts"? - English Language ...
A Wikipedia article tells us that: A problem is regarded as inherently difficult if solving the problem requires a large amount of resources, whatever the algorithm used for solving it. What is a...
Better way to indicate “a large amount of - English Language & Usage ...
Grammar Amount of or number of? We use amount of with uncountable nouns. Number of is used with countable nouns: We use a huge amount of paper in the office every day. The amount of time it took to finish the job was very frustrating. A great number of students volunteer each year for environmental projects. Not: A great amount of students ...