I see your point. The problem with exact numbers is that they are hardly (publicly) available as on the one side, there is the cost of building and running the platform, and on the other, there is potentially lost productivity (which is generally hard to measure). So, for the 2-year development example, I could only rely on the KubeCon talk, and it just mentions costs briefly (saying that it was cheaper for dev teams to use the platform).
Another problem is that it can be very different depending on your situation: If you are currently working with local clusters that are free to use, the direct cost benefits will be much lower than if you use individual clusters for each developer, which are quite expensive even for small teams.
So, I just wanted to give a rough overview of what that drives cost and where you potentially could save money.