There are different insulins. It might be that the expensive ones are still under patent (and genuinely work better than the old ones for many patients). Also,

There are different insulins. It might be that the expensive ones are still under patent (and genuinely work better than the old ones for many patients). Also, it might be that some or all of the insulins are just naturally costly to manufacture, so that when competition is not prevented by patents, the price stays high. (This would be the case for example if the insulin must be extracted from pigs and if each pig yields only a few doses of insulin.) That doesn't contradict the fact that many drugs still under patent sell for 100s of times their cost of manufacture, then when the patent expires the sell price drops to close to the cost of manufacture.