- The "developer cost" is tricky. Salespeople like to pretend that you can calculate that using someone's salary. If you have an $80/hour developer spending five hours on something like this, you don't literally write a check for $400. Instead, that developer might have been doing something useful, but might also have been in a meeting or responding to email or just sitting around. One argument for 20% time is that the 20% spent on that work wouldn't have been used productively anyway.

This is actually a lower bound on the opportunity cost of having your developer work on purchasable items.

- If the dev is making $80/hr they should be adding more value to the organization than $80/hr.

- If 20% of your devs are working on purchasable items you'll need to hire another ~20% to replace them, but then you'll need 20% more managers, QA, etc..

- Developer productivity isn't linear, if you hire twice as many devs you don't get twice as much code written.