Google App Engine, Billing "Minimum Spend $2.10 Per Week"?

Question

When I try to enable billing in app engine for using blob store, I found a notice for Minimum Spend $2.10 Per Week.

The Minimum spend subtotal is in support of our new pricing model. The new model requires that you spend at least $2.10/week. This subtotal indicates the value beyond your other spend that we need to add to your contract. To make the transition to the new model smoother we are beginning to account for this minimum when we authorize new budget changes. Please note that you will not be charged for the minimum spend until our new model takes effect.

I search online and found no one ask about it. I use app engine just for a school assignment, so the usage won't be excess free quota. So, Must I pay $2.10 per week even I do not excess free quota? It sounds unreasonable.

Answer 1

As of April 2013, "We’re happy to announce that billing-enabled applications will no longer be required to spend a minimum of $2.10 per week. This means that you can enable billing for a free tier application and continue running within the free tier without concern that a spike in traffic will terminate serving (note that you can always specify a daily dollar budget). The minimum spend was originally intended to prevent abuse and ensure that we can offer a stable, reliable system with a free tier. We have determined that we can continue to support the free tier, without relying on the minimum spend. So, goodbye $2.10!"

Answer 2

Google has removed the $2.10/week for billing-enabled application from now onwards. You can enable billing for a free tier application and continue running within the free tier without concern that a spike in traffic will terminate serving.

http://googleappengine.blogspot.com/2013/04/app-engine-177-released.html