It depends on the rating. Depending on the rating that occurs on that driver, it could cost to add a person on your policy as an occasional driver. The definition of an occasional driver can vary by state and from one insurance company to the next. Some insurers suggest as a rule of thumb that an occasional driver is not found to be driving the vehicle in question no more than once a week. Anyone that lives in the household or uses the vehicle occasionally should be listed on your policy.
The following is the definition from our website of both occasional driver and principal driver. An occasional driver is the person who is not the primary or principal driver of the vehicle and the definition for principal driver is the person who drives the car most often. These are the general definitions used in the insurance industry.
The requirements for someone to be termed an "occasional, casual or intermittent" driver differ by insurance company and possibly by state so it is best to check with your insurance agent for your specific company's requirements.
That being said generally insurance companies allow coverage for the occasional driver provided that driver does not live in your household and the vehicle is parked at your dwelling at the end of the day. Since this person is being added to the policy to be covered as a driver then yes, normally there will be a cost associated with it.
Not all insurance carriers rate using occasional driver or primary driver. An occasional driver is typically rated at a lower rate than a primary driver by insurance providers that do have these different designations. Also, it may be possible to have a person listed as the primary on one vehicle, but not on all household vehicles.
If you want to add a driver as an occasional driver to your policy you will need to discuss your insurer's definition of this term and how often they say a person can drive a car without being considered more than an occasional driver plus what the cost would be to add a person as an occasional driver to your policy.
It depends on the insurance company and their guidelines as well as their rating systems if it would be cheaper to have someone listed as an occasional driver or primary driver on your vehicle.
Regardless of cost, you will need to tell the use as defined by your specific insurance carrier. So speak with your insurance agent and see if your carrier has both types of driver designations and how they would advise you to add the person you are thinking should be added as an occasional driver.