Cloudflare sells domains at cost. So yes, cheaper than any other registrar (including NameCheap and Porkbun), except maybe those who sell domains at a loss as a promo to rope you in and then kill you on the renewals.
Integration into their stack is a nice side effect, but really inconsequential. You can have your domains registered with any registrar and have your DNS hosted by any DNS hosting provider. Heck, you can run your own DNS servers if you want to.