I don;t think you understand. As a merchant you are selling a computer for $100 on your website coolstufflikethis100dollarcomputer.com
You offer to sell your computer through paypal:
User spends $100 paypal charges 2%+ 0.15 fee* You get 97.85 USD
You offer to sell your computer through Authorize.net's official credit portal
User spend $100 authorize charge 1.9% +0.3 fee* You get 97.80 USD
You offer to sell your computer through coinbase
User spends $100 coinbase charges 1% fee you get 99 USD
So no matter what you use there's going to be a fee, now you could mitigate this by installing the cheapest credit card processor on your website, paypal directly, venmo directly, integrating with apple pay directly, integrating with coinbase directly(or even using your own standalone bitcoind baring the risk of getting hacked) to save the most money or you could just install a few lines of code and have all of those things ready to roll.
I'm not advertising for braintree or paypal just saying this is what happens everyday albeit they cost more but you get more in less time and time is money.
(Also half or more of what braintree colects has to go to their third party processors for each payment option anyway so)
*Fee's guestimated