Do people actually buy research articles? Research articles are often priced at 20-40 USD. I know that typically a researcher's institution subscribes to myriads of journals, and that some research articles are accessible online for free either legally or illegally, but I am curious to know some numbers that would help quantify how many / often individuals buy research articles, and how much money journals make from this source of income.

I am not looking for guesses or opinions, but actual numbers.
I tried digging through the 2013 annual report of Elsevier. Under &quot;Revenue&quot; (page 111) they list both &quot;subscriptions&quot; and &quot;transactional&quot; - but the latter include not only reprints, but also books etc.

As you can see, even if we lump books and reprints together, it is still less than subscriptions.
To get a more complete answer you may have to ask them directly.