The average cost of Medigap Insurance will depend on your age, what state you live in, your smoking status and which Medigap Insurance Plan you have.Medigap Plans can range between $75 per month to $500 per month depending on those factors.The average cost of Medigap Insurance will be different in different states. For example, Texas, South Carolina, North Carolina and Colorado are usually less expensive than South Florida.However, North Florida will generally be less expensive than South Florida.he cost of a Medigap plan will be determined by several factors-your age, your gender, your zip code, any tobacco usage, and if you and a spouse are applying together (some carriers offer a household discount on their rates when spouses apply for coverage at the same time).