Right now Porkbun has the cheapest first year at $4.63, and Porkbun the cheapest renewal at $31.41. Over three years the lowest total at one registrar is $67.45 at Porkbun.
Why does .diy cost more after the first year?
Many registrars sell the first year below cost and recover it at renewal: at Porkbun, .diy renews at $31.41 after a $4.63 first year. Compare the renewal and 3-year columns before you buy.