A new item attribute, say Month could be created with an attribute value for each month, then an Item master for the service, adding multiple variants based on month. A time saver? Probably not for a one time item, however if you provide other services monthly the attribute could be reused.
I don’t know what happens if you add or remove an attribute from a master, once the item variants have been committed to transactions. I suspect adding attributes wouldn’t matter, removing them might not either but without creating a test I can’t say for sure.