You are on YC's forum!
I suggest you learn how the price of a product or service changes based on regulation, cost of employees, the amount of money a business owes in loans, basic stuff!
More overhead adds to the cost.
A smart contract infrastructure will not have zero overhead, but it will be close to it. Much less than a centralized service provider.
There is no "middlemen" but more just one "middleman" which is the smart contract which each will have a different protocol and how they handle fees.
Some will use it to pay for API calls, others will use it to do some automated token buy-backs. Depends on the contract. And the beauty is, the contracts are all publicly available so you can read it before requesting to the service.