So, App Engine announced new pricing. It looks to be more expensive, and many would say this is an understatement. It is more expensive, and/but you can probably take some steps to manage and design for the pricing model. What you need to keep in mind is that "instances" are now a fundamental pricing component, where they weren't before. Managing instances thru latency and caching to reduce instance use are directions you need to consider. Here are two useful articles:
Look at using caching and datastore more efficiently, and use the Admin console to experiment with the scheduler. In particular, the "Lower Max Idle Instances" is a good place to start. Check the managing-resources article above for more details. I expect that more information will be forthcoming as well.
UPDATE: I expected more, but who knew this soon. From Peter Magnusson who is director of the AppEngine team, read his Google+ post for more context.
Minor note: glad to see Python 2.7 about to be rolled out.