There's no insulin that is 100 years old that diabetics use. The insulin used is of many types and all these types have been developed over the 100 years you seem to ignore, and new ones are still being developed. You can now buy inhaled insulin. There's rapid acting and medium and fast and super fast and there's mixes developed for certain patient groups.

There is no reason for insulin to cost 300USD when competition can make it for 10USD.