Right now Porkbun has the cheapest first year at $4.63, and Hello.co the cheapest renewal at $9.00. Over three years the lowest total at one registrar is $27.00 at Hello.co.
Why does .one cost more after the first year?
Many registrars sell the first year below cost and recover it at renewal: at Porkbun, .one renews at $20.08 after a $4.63 first year. Compare the renewal and 3-year columns before you buy.