They must have different definitions for "at cost". Cloudflare charges the wholesale registry cost plus the ICANN fee. According to their blog post, Porkbun charges a price that would allow them to break even, which also includes regulatory taxes and payment processing fees. Since Cloudflare doesn't factor in these additional taxes and fees, they're losing a little bit of money for each domain they sell. I guess Cloudflare considers this a marketing expense to promote their CDN and other paid services.
Cloudflare is the least expensive registar, but they don't handle new domain registrations (only transfers and renewals), and they offer fewer TLDs than Porkbun. A combination of Cloudflare and Porkbun is the most cost-effective way to register domains in the long run, unless you're willing to deal with registrars that steeply discount only the first year.
I see, thanks for the info. Btw, Cloudflare do offer new registration now, though it's currently marked as "beta", maybe only certain accounts have access to it.
Cloudflare is the least expensive registar, but they don't handle new domain registrations (only transfers and renewals), and they offer fewer TLDs than Porkbun. A combination of Cloudflare and Porkbun is the most cost-effective way to register domains in the long run, unless you're willing to deal with registrars that steeply discount only the first year.