I think you missing the point. As you say there is no way to know for sure what the ‘correct’ price is for your product. One customer may be willing to pay $X and another $5X for the same features, but you need to find the number that maximises your profits across your whole customer base. As such most companies effectively just pluck a number out of the air and see what works.
Patio11’s argument is that most companies are charging a safe number that works, however that number is too low. By charging more, yes you will scare away some customers, but the customers who are concerned about price aren’t the customers you want.
In your case, say you cloned something like SendGrid and charged half the price. Their big customers like Airbnb or Uber effectively don’t care how much an email costs to send, they just want to guarantee that it is sent. So if you manage to score a customer like that, you are leaving a lot of money on the table.
On the other hand, the customers that do care about price are likely going to be lower quality, maybe they are sending bulk newsletters which if marked as spam will damage your company (as your IPs will end up on blacklists) - meaning more work, and more cost, cleaning up their mess.