Right now Regery has the cheapest first year at $6.99, and Porkbun the cheapest renewal at $7.43. Over three years the lowest total at one registrar is $22.29 at Porkbun.
Why does .みんな cost more after the first year?
Many registrars sell the first year below cost and recover it at renewal: at Regery, .みんな renews at $8.99 after a $6.99 first year. Compare the renewal and 3-year columns before you buy.