How costly are triggers mantaining an extra Collection?

Hi! I’m developing an app that use private and public data. Private is maintained normally using partitions. My idea is to have basically a public copy of a collection that can be read with any user.

For example, imagine an private collection called Contact with a boolean field called published. When this is true, a trigger will upsert in a new collection called PublicContact with the data. This collection will be able to be read by anybody. If that published field is set to false, the trigger will just delete it. The same if the contact is updated, the trigger will update the public record.

Now, I just want to know if this is a good way to manage this kind of stuff and how costly it is (talking about billing, of course).