If you're trying to get your head around the difference between back up & business continuity, it ultimately comes down to downtime. How much can your business tolerate?
We strongly recommend every SMB has business continuity in place. Traditional back up isn't enough anymore to protect against all the cyber-threats that continuously try to push their way into your business.
Of course there's a cost, but in the long run you have peace of mind knowing you won't be losing days, weeks or even months of data if your business gets hit. Imagine how costly that would be.