The primary cost for domains is potential downtime. How much does a day of downtime cost you and your company? I don't want to think about it either.
The next most significant cost is labor - your time and your business' delays when dealing with the registrar over service and support issues.
Both of these problems are solved with available, responsive, highly effective support. If it goes down, you want to reach someone right away who has the skill to quickly solve the problem and who is empowered to do whatever is necessary to bring it back up. And for lesser issues, quality support means you spend less time solving problems, which not only saves you time and frustration but reduces delays for your work that depends on the problem, and for other people depending on you and people depending on those people. It's the difference between spending days trying to communicate with someone who turns out not to understand the technology anyway, and then you have to figure out a solution yourself and coax them into implementing it, and communicating with someone who answers immediately and says 'I got it', explains the tech to you - and you don't bother to remember it because they already know it.
I don't see support, the most important capability of a registrar (besides basic competence) IMHO, mentioned in Cloudflare's announcement. What is the support story?
EDIT: Added exposition