[slowmovintarget]

You forgot the cost of Y hours your developers could have spent on A.

This is the actual, non-cynical driver for many of these decisions. An exec is looking at devoting developer time to building or curating software that isn't part of the core competency of the business, and balancing it against staffing product development or IT aimed at the business's specialization.

To make avoidance of E palatable, you have to show that use of O will not only cost significantly less that E, but that using it will also make up for the lost time that you would have spent building A.

I say this as someone who constantly has to justify why we don't just grab some SaaS offering off the shelf and groom it * cough * um... integrate it, rather than continuing investment in the purpose-built "commodity" my team runs.