When have customers ever been happy about a price increase? Right. So it should come as little shock that there’s a bit of grumbling about Google App Engine (GAE) prices going up as it leaves preview. It’s not just the pricing increase, though, Google is also changing the way it calculates the bill.

To mollify customers a bit, Google is extending a one-time credit of $50 through October 31st. Given the feedback so far that may not be enough.

Google’s new pricing model does away with billing by CPU time, and now charges by on-demand frontend instances. Google (fairly) says that it’s made the change because CPU time is just one aspect of resources used by App Engine. “When App Engine runs your code, it creates an instance with a maximum amount of CPU and memory that can be used for running a set of your code. Even if the CPU is not currently working due to waiting for responses, the instance is still resident and considered “in use”.

While it’s undoubtedly true that there’s more than CPU to consider, the change in pricing seems to be leaving GAE users with sticker shock. Comparing pricing from one PaaS or cloud service provider to another’s has never been easy. But comparing Google’s old and new pricing is no easy matter either. Bandwidth prices have remained the same, but the switch from CPU time to instances makes it difficult to do the conversion. One response over on Hacker News indicates that the expected bill will go from $9 a month to $270 a month.

This has raised charges that Google is bait and switching its users. Google App Engine has been in preview for more than three years. It launched in April of 2008, and was one of the first Platform-as-a-Service (PaaS) plays. It launched in closed beta to about 10,000 developers getting early access to free (but limited) resources. Since then it introduced pricing that seems to have been found reasonable by quite a few developers and organizations.

Google has had three years to figure out its pricing, so this seems like a pretty drastic change. And GAE customers may be in a worse position when it comes to moving – its APIs and software stack are unique, so just picking up and moving to another service is not an easy option. One user makes the point that while Google may not raise the price often, it might be safer to go with providers with more standardized software stacks. “That way I can take advantage of future competition of providers.”

In fairness, Google has also added a few perks as the service is leaving preview. For instance, the company is now adding Service Level Agreements (SLAs) to the Paid and Premium levels of GAE, and operational support to Premium accounts. Only Google knows for sure whether the pricing model is necessary to make GAE a sustainable service on their end.

But the switch has the potential to hit current GAE users in the pocketbook, perhaps hard. Is Google gouging its GAE customers, or just making necessary adjustments? Let us know what you think, and if you’re being affected by the change.