The cheapest credit card processing for a small business is the setup that produces the lowest effective rate on your real sales, not the lowest advertised rate. Rates differ by card, by processor and over time.
Avendo's approach is to stop choosing one processor for every sale. Its platform connects your existing checkout to multiple PCI DSS-compliant processors and routes each transaction to the one offering the best available rate in real time. Avendo says it does not bill merchants directly; its compensation is handled between Avendo and the processors. Its homepage does not state a price, so ask Avendo how this applies to you.
Who might pick something else? A business that values one simple flat rate above all, or one that sells almost entirely in person, may prefer a single provider. See the small business processing guide for a fair comparison, or the payment processing reporting guide for how to track costs month to month.