We have currently an enterprise subscription. Can we create a second enterprise organization and share collections/passwords between them? Must a user have an account in both organizations? Will the second organization billed differently and does it have a different cost for new users?
If it is not possible, we can integrated the departments within different collections/groups.
I believe you are correct that there is not an easy way to share items/collections between two separate Organizations.
Typically each organization would act as its own separate entity and users would need to be a member of both organizations to have access to relevant data.
You are also correct in your assumption that a secondary Org would have additional cost associated with it as well.
Using groups to assign collections is definitely the way to go. This can also be automated with the directory connector desktop app or CLI for teams and enterprise, or alternatively with SCIM for enterprise organizations.
I would recommend reaching out to contact the Bitwarden support team and they should be more than happy to assist with any questions and setup you may have.