Right. Surprisingly, the comment you're responding to resembles some of my clients. This is a business problem.
In this case it's not "save us a few grand" that they're asking for-- the real ask is "help us analyze and forecast our spend as we continue to grow." Identify the knobs and dials that impact infrastructure costs, devise a costing model that states "each additional user costs $X to service," identify what makes sense to arbitrage between AWS and other providers / on-prem...
If I'm being honest, "lower the bill" is where it starts, but not nearly where it ends. :-)
Remember that he has to charge at least $1000 a day. He's more expensive than your entire bill.