Give me read access to a $50,000/month AWS account and I will tell you within a day where the first 20-30% is hiding, because on a mid-size bill it is almost always hiding in the same four places, in the same order: data transfer you can't see in the console, instances sized for a load test that ran two years ago, on-demand pricing on a baseline that never moves, and storage rotting in the most expensive class AWS sells. None of this needs an architecture rewrite. AWS cost optimization, at least...