I Am An Insurance Agent Working With A Client On

I am an insurance agent working with a client on selecting a Medicare Part D drug plan. One of his meds is metformin OSM ER 1000mg. B.I.D. According to Medicare's website the osmotic metformin costs a small fortune vs. regular metformin, non-osmotic, which is quite cheap ($450.00/mo vs. $10.00/month). Does a 1000mg ER metformin have to be osmotic, or is there a 1000mg metformin ER that is not osmotic, and therefore not costing a small fortune?