Right now Porkbun has the cheapest first year at $4.61, and Porkbun the cheapest renewal at $5.64. Over three years the lowest total at one registrar is $15.89 at Porkbun.
Why does .download cost more after the first year?
Many registrars sell the first year below cost and recover it at renewal: at Porkbun, .download renews at $5.64 after a $4.61 first year. Compare the renewal and 3-year columns before you buy.