I lost my right AirPod

In the U.S.? If so, $69 (or $89 for AirPods Pro).

For other countries and for more information, see the following from Find your lost AirPods - Apple Support

Replace a missing AirPod or charging case

If you still can't find your AirPod or charging case, or if something is damaged, get the serial number and then contact Apple Support for a replacement. Then learn how to set up your replacement.

Learn more about AirPods pricing and service options