If there is one thing that I have learnt from "Predictably Irrational" book, it is that humans make their money-related decisions by having a reference point. Zendesk could have always been priced at thousand bucks and no one would have complained. But once you set the price, you provide your customers with a reference point which they are going to use. You can't run away from that.

For example, even though Microsoft Office probably provides a lot more value than what it costs, it they doubled their prices overnight, would you not expect any outrage?