It's not about the fact that prices are rising. In my country it's a constant process, they never stop. It's about:
1. That the gap between old and new prices is 50% which is a lot. I don't see many businesses do this to their loyal clients. We would understand something about 15-20%, not 50%.
2. That you guys try to sell it like "but look at monthly rate! Not a big deal!". You seem to forget that people who are able to spend hundreds of dollars on forum software are adults and wouldn't fall to cheap marketing tricks. I'm a marketer myself, and I know exactly what is happening here.
3. That you didn't inform us before this decision so any hobbyists could pay for their software. The greediness is not good.
4. That you try to sell it like IPS is the best thing ever, some premium software that is nowhere near it's competitors. But would the best software company treat it's customers like this? For real?
5. That you tried to cover it under website redesign.
6. That you're telling us "pay more but if you have a problem - go ask community"
You know, it feels really bad. It's a really bad publicity. How many existing clients will recommend IPS after moves like this, how do you think?