[alexchamberlain]

How does that $0.21 compare to the cost of maintaining the coin machine on a vending machine and sending someone to collect the cash?

[mytailorisrich]

The difference between fixed and marginal costs applies here.

The costs you mention are essentially fixed costs. The marginal cost of a sale is then zero (ignoring the cost of the item itself).

With Stripe the marginal cost is 21c or 42%. You can increase sales ad infinitum and Stripe will still take 42%...