I'm finishing up a course of amoxicillin, which is so cheap that my local grocery store pharmacy just gives it away for free as a form of advertising. But how much did it cost when it first came out? All I have found is this which is $20/unit down to 55c after production ramped up. But how many doses did you need? How much did the cost of a full course of it compare to an average family's income for the wartime in America?
Your source is actually quoting $20 per 100000 units, not per unit. Which is a good thing, as a typical dose of iv penicillin is anywhere from 4 million to 24 million units a day depending on what's being treated. I'm not sure if these modern doses are the same as those they'd have used in the 1940s, though. Assuming 1 million units four times a day for a week of treatment gives us a treatment course of 28 million units, at a cost of $5600.
What's that equivalent today? According to this calculator, anywhere from $70000 to $750000! If you use the method of comparing it to average wages of the time, which makes sense to me, it's the equivalent of $230000 in terms of a skilled factory worker's wages.