Online NAS backups

Hi! I am kind of new to this so I am not sure I put this in the right subsection. I am thinking about setting up a NAS for backup of a number of computers (Mac, Linux, Windows) and I had been thinking about a RAID 1 setup to make sure that my data was secure, but two large drives gets very expensive, and it would not be off site. What I was wondering is I know that you can buy fairly cheap unlimited online backup, but could I set up my NAS to automatically backup all files to that once a week for example or continually only uploading the new stuff?

Thanks!