I am actually a SQL server DBA in real life. My recommendation is to enable compression for your backup and also enable trace flag 3042 in SQL Server to use a different backup pre-allocation algorithm that uses less disk space. see https://docs.microsoft.com/en-us/sql/t-sql/database-console-commands/dbcc-traceon-trace-flags-transact-sql?view=sql-server-ver15 for additional info. Backup compression is simply an argument in the BACKUP command, so very easy to implement.
the streaming to s3 solution @rafaelchei posted is interesting, but wouldn't use Rclone as it directly interacts with S3 storage instead of using the rclone mounted volume.
you should also be aware that SQL Server has native support for Azure blob storage directly from the backup command. This would be simple to implement and is roughly the same cost as AWS blob storage, but is built into SQL Server and requires no additional software or config. something to think about if you are just looking for a cloud storage destination for SQL Server backups.