http://alexgorale.com/bitcoin-block-size-riskThis is 10x the maintenance cost of today. Forgoing the block reward and relying entirely on transaction fees to fund a multi-billion dollar network brings the entrance cost of a transaction to $21.
That $21 fee is for the 500,000 or so transactions that occur every day. This number is only the floor. It represents what it hypothetically costs to run the network assuming no one tries to outbid each other. $21 is the price of a transaction for the first half million transactions each day. Each transaction after that waits until the next day or, if it includes a higher mining fee, bumps lower fee transactions down in the queue. Still, that 500,000 transactions is not enough to represent the 3 billion internet users online today.