I realize that there's many HN Members who may be trying to start a company in 3rd world countries where $30 is a significant chunk of change, and this may sound harsh. But if your business, at any point, can't absorb a $30 a month increase in fees for something as important as your subscription billing system then something is wrong.
I am not really sure it's the price change that is most offensive. It's the fact they were willing to do it without regard for their current customers. I don't want to deal with a company that is happy to change their price whenever they feel like it and I get the short end of the stick.
Trust me, we weren't happy about having to raise the price. It was a painful, hard-fought decision to change it internally, and to not permanently grandfather existing customers. But in the end it's about having a sustainable business - the worst possible outcome for customers is for the service they were powering their billing with to disappear altogether.
Sure it can absorb a $30/month increase in fees. But if multiple service providers hit me with a $30/month increase then it kind of adds up. In other words, a price increase like this is ok as long as it's the only one.