Insulins are biologic medicines, so once patents expire you might get biosimilar drugs which also require FDA approval, not generics as with other drugs. Admelog is the biosimilar for Humalog, approved by the FDA in early 2018.

As I understand it, Sanofi (Admelog's manufacturer) sets the price to be only slightly below that of Humalog.

Eli Lilly, Novo Nordisk, and Sanofi manufacture substantially all of the insulin, and they more or less follow each other price-wise. There's not the competition you would expect that would drive down prices.

EDIT: they compete by offering varying discounts to particular insurance companies to only cover their insulin at the exclusion of the other company's insulins. This often leads to a letter to patients near the end of the year telling them that the insurance company has decided that their treatment plan has now changed, decisions of their doctor be damned. (Yes, you can appeal and what-not, but it's still fundamentally the insurance company's decision, not your doctor.) This, of course, also screws anyone without insurance who is expected to pay list price.