I have disabled Google App Engine billing for AWSQS, and for now it looks like it is handling the load fine as a strictly "free" app. However, various resource quotas will change when the new pricing goes into effect, so only time will tell if this will be a viable approach. Total capacity should be around 2M requests per day, which was only hit once when an apparent DOS attack occurred.
In other news, GAE is saying that the new pricing structure will not go into effect before September 26, for whatever that's worth.