As for why it’s 77 cents, maybe the price isn’t flat, but instead, the amount is based on when the registrar contract is signed.
Verisign (initially) knew October was when Cloudflare would open the registrar business.
The month of October is 83% of the year done.
since the price increases 10% yearly, $0.902 would be added to the price upon the date of February 2019.
83% of $0.902 is ~$0.75
$9.02 + $0.75 = $9.77
^The above is probably not how it’s actually calculated but shrug.
As for why/how other registrars have cheap prices, many of then take the blow for the cost up-front for the initial registration (like how GoDaddy can offer new customers .com for $1) but then they make it back by doing something like charging higher renewal rates, pushing their other services (hosting, email), etc.
Cloudflare doesn’t making any money off of registration/renewal by hoping that you’ll upgrade the domain to the premium plan in the future.