The cost for me to transfer a $20 bill to someone to buy a cup of coffee is zero. The transaction time is 0ms. There are zero confirmations needed.

The cost for me to transfer $20 to someone in the form of a check is zero. The transaction time is 0ms. The money does not show up immediately, however, and there is counterparty risk if I don't have the money in my account.

The to transfer $20 to someone in the form of a credit card payment is $0 to the buyer. In fact, the buyer can get cash back on their purchases. Credit card costs are incurred by the seller. Small businesses bitch about their merchant fee they pay. Larger merchants pay almost no merchant fee. The fees are negotiated and the customer generally doesn't see them. The advantage to the merchant is that the customer doesn't need to have the money to buy their goods or services because with a credit card, the money is borrowed money. A person can buy a $500 pair of shoes when they have $50 in their bank account and pay back over time. That means the merchant will have more buyers for their products than otherwise. The transaction time is a second or two however, it takes time to clear to the merchants account.

The cost of ACH transfer (eCheck) from bank accounts is generally zero.

The cost for me to transfer $1MM to someone via wire transfer is zero for me. I get free wire transfers because I maintain a high balance. For normal accounts, the cost is $30 or so. Wire transfers are generally irreversible but there is a legal trail so the receiving party can't say "we didn't get your money". They are not immediate, they take a day or so. But they are generally only used for large transaction amounts.