There is always a cost
All depends on how much you value your stuff - if a loss of data is of little consequence, you need not even back up. However, if such loss would cause you pain, then making backups one way or another is desirable. Both your computer and its OS have limitations in this area (read: risks). Buying a huge external HDD plus good backup software can be just the ticket, with a price tag. Consider the potential level of pain, and cough up accordingly. You get what you pay for.