Right now Dynadot has the cheapest first year at $7.99, and Dynadot the cheapest renewal at $9.99. Over three years the lowest total at one registrar is $27.97 at Dynadot.
Why does .co.im cost more after the first year?
Many registrars sell the first year below cost and recover it at renewal: at Dynadot, .co.im renews at $9.99 after a $7.99 first year. Compare the renewal and 3-year columns before you buy.