What are your peak memory, cpu, and bandwidth requirements? GAE is expensive for what you get. Have you considered dedicated hardware to offset hosting costs?
I'm using GCE (=Google Compute Engine), not GAE. I considered using GAE long ago (seriously testing it and writing a first version), but was scared off by the vendor lock in. I don't want anything to fundamentally depend on a 100% open stack. GCE's pricing is competitive with AWS and Azure.
I did run SageMathCloud on a lot of dedicated hardware that I hosted at Univ of Washington from March 2013 until May 2015, but had to stop due to University rules. I had planned to buy computers and rent hosting in a data center, but when I looked into the costs of commercial dedicated hosting, bandwidth, and the time and people required to maintain physical hardware with the availability requirements I have, it started looking much worse than using GCE (especially as GCE prices kept dropping). I don't have any employees at all, so when something goes wrong with the hardware, I would have to drive there and fix it myself. What if asleep or traveling across country? No matter what, the odds GCE will fix any problem in a timely manner is much higher than the chances I will. The middleground is something like Rackspace, etc., which doesn't look that much better regarding cost than GCE. Of course, the price of hosting on GCE is a lower order term compared to the price it would cost to pay myself to admin everything, if I wasn't doing it in my spare time.... and then there is development work too.
I did run SageMathCloud on a lot of dedicated hardware that I hosted at Univ of Washington from March 2013 until May 2015, but had to stop due to University rules. I had planned to buy computers and rent hosting in a data center, but when I looked into the costs of commercial dedicated hosting, bandwidth, and the time and people required to maintain physical hardware with the availability requirements I have, it started looking much worse than using GCE (especially as GCE prices kept dropping). I don't have any employees at all, so when something goes wrong with the hardware, I would have to drive there and fix it myself. What if asleep or traveling across country? No matter what, the odds GCE will fix any problem in a timely manner is much higher than the chances I will. The middleground is something like Rackspace, etc., which doesn't look that much better regarding cost than GCE. Of course, the price of hosting on GCE is a lower order term compared to the price it would cost to pay myself to admin everything, if I wasn't doing it in my spare time.... and then there is development work too.