Replacing a freezer seal only costs the price of the seal if the homeowner does it himself, and prices range from about $20 for a universal gasket to $80 for a brand-specific gasket, as of 2015. Having a repair professional install it also incurs the price of a service call.
Before putting a new freezer seal into place, it helps to soak it in hot water for at least an hour. This gets rid of the creases that packaging leaves behind. Checking how the old seal was attached shows where the new seal attaches. After drying the new seal, replacing it using the same fasteners, or at least fastening it in the same places, completes the process.