If you walked into your office tomorrow and found your on-site back up destroyed by fire or flood what happens next and how long before your business is functional again? Just having a "back up" isn't enough these days especially as weather patterns evolve. But you say it's all you can afford, but if the backup is IN your office, can you afford to lose your hardware AND ALL your data? That's a single point of failure, leaving zero protection from theft, fire, flood or a major natural disaster.
Studies show that a disappointing 6% of businesses survive a major data loss event. A massive 51% go out of business within a two year period, and 43% of them close their doors immediately. These stats matter since many businesses feel a false sense of protection because they feel they are too small. But when you calculate the downtime, it starts to add up.