Right now Porkbun has the cheapest first year at $1.54, and Epik the cheapest renewal at $30.43. Over three years the lowest total at one registrar is $64.36 at Porkbun.
Why does .forum cost more after the first year?
Many registrars sell the first year below cost and recover it at renewal: at Porkbun, .forum renews at $31.41 after a $1.54 first year. Compare the renewal and 3-year columns before you buy.