Lock change vs rekey
They solve different problems, and picking the wrong one is the most common way to overpay on a door.
Change the lock when the hardware has failed
Change it when the deadbolt drags or will not throw fully, when the handle wobbles on its rose, when the cylinder is corroded from coastal damp, when the finish has gone, or when you are moving up a grade: a builder-grade knob to a Grade 1 deadbolt, or a standard cylinder to a restricted keyway. A lock change is $80-$160 a door installed.
Rekey when the lock is fine and only the keys are wrong
Rekey after a move, a tenant change, a lost key, a contractor who never gave the spare back. The pins inside the existing cylinder are restacked to a new key and every old key stops working. That is $25-$45 per standard cylinder, $60-$120 for a high-security cylinder, and the hardware on the door never changes. Full detail on lock rekey in Vancouver.
Rule of thumb: if the lock still turns smoothly with its own key, rekey it. If it fights you, replace it.