I'm not saying it can't be done cheaper or more efficiently on simpler providers or even self-hosting, but you need the expertise and time to stand up the foundation of a secure platform yourself then. For example, AWS Secrets Manager is just there and ready to code against, as opposed to standing up a Vault service and working through all of the configuration oddities before you can even start integrating secrets management into an application. If you already have a configuration-in-a-box that you can scale up, then more power to you.

Your use-case of running a web service that is written in a very efficient language like C++ is not something you see too much these days. While it would be nice if most devs could pump out services built on performant tech stacks, our industry isn't doing things that way for a reason. Even high-prestige companies with loads of talented engineers only build select parts of their systems using low-level languages.