Hey, this looks really cool! I've been working on a very similar product: https://cloudcosts.io/. It's only hosted, no open source versions of the software and much simpler.

It has a few users and I haven't figured out yet if it could be monetized. The basic thing that I wanted was a daily email of my cost changes from AWS.

How have you found trying to integrate Google Cloud and AWS billing? That's where the real value in this type of product is to me.