I often wondered about things like this: how much does the installing, maintainting and controlling a payment process (including but not limited to technology)

I often wondered about things like this: how much does the installing, maintainting and controlling a payment process (including but not limited to technology) contribute to the overall cost of a service? And would making that service free reduce its cost so much that for instance a free lunch would actually cost less than a cheap lunch to the provider of that lunch?