Are those blob storage options significantly cheaper than Google? I fear we are being pushing down a GCP route as it is what out consultancy know, rather than the best solution.
R2 would probably be significantly cheaper because they don't bill for bandwidth, but S3, GCP storage, and Azure storage would likely be in the same ballpark. Blob storage is a commodity service, so the major providers mostly match each other's prices and features.
If you are already using a particular cloud provider for the web application that will be accessing these documents, you should use their blob storage unless you have a compelling reason not to. Communication between a cloud provider's compute and storage services within the same region will have minimal latency.
