My key argument when I've convinced past employers to implement it: you already outsource all of the hard parts of your security. Antivirus, firewall, AD permissions, server config, all of it. They either bought a product to fit the need or hired a consultant to do the advanced stuff. $12/year is pretty cheap to hire a dedicated team of security wonks to safeguard your passwords, IMO.
It's not the cost that's the issue though, people don't like the idea of passwords being stored in a single place on a internet connected computer. I mention that you can secure password access behind two factor authentication but it doesn't get around the knee-jerk reaction often. Sharing lots of passwords when working with a team remotely is especially painful when password managers are not allowed...
