Getting custom software developed on the surface can seem like a very simple thing. The customer sees something that he needs and wants it done. However, what the customer may not realize is what is involved which in turn equates to the cost of getting customized software developed.
Custom software can be a rather tedious process. It involves a lot of details and these details should be outlined on paper. Depending on the client's needs, that can determine which approach may be best. In many cases there are off the shelf software that allows a developer to make modifications to it.
However, when it comes to modifying existing software packages a lot of factors also depend on what the vender allows a developer to do with their proprietary software and any development kit that is part of their software.