Is there a calculation I can do to figure out how much money 20,000 pages read gives me?
I know it's calculated on a monthly basis - so going by last month, what would 20,000 pages read work out to be?
Since you mentioned a round number, you should know this: don't expect that to continue.
For books published over the past 7 to 10 days, there was a bug in setting the KENPC for some books. When that happens, KDP assigns a placeholder of 500 pages read each time somebody reads the book, regardless of how many actual pages were read. Sooner or later, they'll fix the problem and correct the numbers, though, so enjoy it while it lasts.