You can share selected photos to the Shared Library from your personal iCloud Photos Library. The problem is, that all photos from the personal iCloud Photos Library will be stored in iCloud Photos. There is no way around this - iCloud Photos is all or nothing. So you have to keep the personal iCloud Photos Library small, where you are storing the photos that will be shared to your Shared iCloud Photos Library. Keep all other photos in additional archive libraries. Only one library can be syncing with iCloud Photos at a time. The person, who is setting up the shared Library will have to pay for the cloud storage. Invite only people to your shared library, who can be trusted to share only a few, selected photos and not to be flooding your shared library with thousands of boring and redundant photos and videos.
I am sharing my Shared iCloud Photos Library only with myself. It is great way to have my most important photos in two different iCloud Photos Library. I have a larger iCloud Photos Library, an archive of many photos and videos, syncing with my Media and Purchases Apple ID on all my Macs, and a smaller iCloud Photos Library syncing with my iCloud Apple ID, used on my iPad and iPhone.
To create additional libraries, see: Create additional photo libraries in Photos on Mac – Apple Support (UK)