User group specific location based directories

[ Moderator note: moved to Fixing WordPress. Please do not use Developing With WordPress for these topics. ]

So here’s what I’m hoping to find a way to accomplish.. I’m getting ready to build a directory listing site that would display specific locations on a map, with listing info pages. I’ve found several great plugins for this, but I need to have user groups, where a business will sign up so that their employees can access this directory, add listings, etc. Now, I need it so that each business/ group will have their own directory. The public and other groups can’t access it, and they can’t access other group’s directories. So group A will be able to add listings that are visible and editable by their group, group B will add their own listings, and neither group will even know the other group’s listings exist. I thought of doing a multisite setup so each group just has their own site that’s a clone of the original, but I’m hoping to be able to avoid that.
I really just need some ideas, not necessarily the specific instructions to do it. Maybe somehow set it up with buddypress? I really have no idea where to start…