Ok, I am not going to do a point by point pricing comparison to Google App Engine, but it appears that Visual Studio is a much better price.
Here are the pricing for Visual Studio:
Express versions: Free for any number of executable, infinitely scalable for no additional cost, which for the Google App Engine isn’t a component of the free component.
And what the use of Java? Ok, we all write Java, but who owns Java? Who owns C#?
Java is owned by Oracle Corporation, and they have proven this by their legal suit against Google, so this means that you can’t use Java with confidence that google will maintain Java forever. There are no specifications for Java, Oracle can do what they want with it.
Who owns C#? No one, it is a specification based language just like C++, C, and ECMAScript.
You decide. But you can use C# for no cost and you can scale your application infinitely for no cost.
Sounds like C# is the better deal.