A domain is a yearly bill, not a one-time purchase. Registrars often advertise a low first-year price and then renew at several times that amount. A $1 first year followed by $20 renewals costs more after three years than a flat $12 price, and transferring away later adds fees.
DomRenew lists renewal next to register and transfer, ranks TLDs by holding cost, and flags extensions where the renewal markup is steep.