A great example of this is [Firebase Storage](https://firebase.google.com/docs/storage/). We've made the 90% of file upload/download use cases easy, while making the 10% of use cases (lifecycle management, object versioning, advanced processing) [accessible through Cloud](https://firebase.google.com/docs/storage/gcp-integration). Stay tuned for more, similar integrations in the future :)
As for the financial costs--you're paying someone else to build and manage your infrastructure, so yes, it will cost more than buying raw infra. Again, this is a tradeoff: is this more valuable to your product/users to answer pages or build features? Depending on where you are in your product lifecycle, YMMV.
(Disclosure: I work on Firebase)