Software is all about data. Asses how much risk the data in your application carries with it. How important is it? What will happen if your security is broken and the data get out on the street? Think about the privacy of your users and the company image.
Asses the risk and make sure your security is strong enough to mitigate it. A higher risk leads to a stronger security (which leads to higher costs, but if you can prove this to your business, they are likely to prefer paying the price of being secure in stead of picking up the pieces afterward).