It depends on the volume of data. Running a second Synology unit at another site and mirroring changes (using something approaching the efficiency of rsync) will easily be the most economical beyond 1tb -- an amount typically included for free with just about every Office 365 subscription. It's not ideal however, unless you plan to perform DR to the cloud; that is, restore a failed local instance to a cloud platform. This is because you will be unable to get one tenth of 1tb of data that stored in the cloud in a timely fashion unless it is being restored to an adjacent platform.
Backblaze Synology
The cool thing about rsync is that the bandwidth use can be near zero as you can do a full mirror once a week but generate a differential file each night and export it to a local drive instead of applying the changes over the internet. That differential file can be used to roll the remote version forward to the time the file was generated. You would only actually apply it to the remote mirror if need be -- testing notwithstanding.
Backblaze And Synology
How to Connect Your Synology NAS to Backblaze B2 Cloud Storage. Back Up and Restore Time Machine Using Synology and the Backblaze B2 Cloud. Support Article. How to Use Synology Hyper Backup with Backblaze B2. Support Article. Encrypting and Decrypting Files via Synology Cloud Sync. If you’re looking for an alternative I would suggest checking out Backblaze and the post How to install Backblaze on Synology NAS. Install headless CrashPlan on Synology NAS. These steps are being done using a Synology DS412+ running DSM 5.0 Update 7. (Tested to work on latest DSM 6.1).