Right now Porkbun has the cheapest first year at $1.54, and Epik the cheapest renewal at $50.43. Over three years the lowest total at one registrar is $105.56 at Porkbun.
Why does .baby cost more after the first year?
Many registrars sell the first year below cost and recover it at renewal: at Porkbun, .baby renews at $52.01 after a $1.54 first year. Compare the renewal and 3-year columns before you buy.