The current top-shelf insulins were not discovered in the 1920s and are considerably better than the ones that were. The older insulins (going back to R, L, N sold in the 80s) are fairly inexpensive; on the order of $25 per bottle (and I believe can be bought over the counter). The newer insulins sell for on the order of $275 per bottle.

The numbers I see say it should cost about $300 for a years supply for me (given my current usage) if everything was optimal (non-greedy, short supply chain). Then assume it goes through 3 hands to get to me (original manufacturer, distributor, plan manager; I'm ignoring the pharmacy since I assume they're at least partially altruistic) and add 50% each time for a total of 1012.50 (300 * 1.5. * 1.5 * 1.5). So even then, it's still less than 100 per month expected cost. Though that's for only the short acting insulin, not the 24hour.

What it would really cost without insurance right now is thousands per month. They're making bank on it.