Robust User Permissions

I am working on a WordPress e-commerce site.

The goal is for user permissions to be very specific, so that different clients will see entirely different pages and content when they log in.

For instance, Client A would see five pages of content specific to Company A, whereas Client B would see five completely different pages (albeit build from the same templates) specific to Company B.

This plugin looks as though it might serve that purpose, but I’m willing to do more grunt work to build something less expensive.

Your ideas are appreciated!