Depends on what type of locker. Case lockers are more expensive as they replace the case and require gear setup. Lunchbox lockers replace the side and axle gears inside the case and require no gear setup.
Lunchbox lockers, I have 2 pr of discs with teeth that mate together and use pins/springs to keep operating. I would check to make sure the edges of the teeth are still cut straight and not rounded. Most of the time, a spring may get broken and this ratchets the discs/teeth. New pins/spring kits are under $20.