Right now internet.bs has the cheapest first year at $19.03, and Regery the cheapest renewal at $36.99. Over three years the lowest total at one registrar is $110.97 at Regery.
Why does .bi cost more after the first year?
Many registrars sell the first year below cost and recover it at renewal: at internet.bs, .bi renews at $75.49 after a $19.03 first year. Compare the renewal and 3-year columns before you buy.