jonesing

I've been using digital certificates at work for our internal sites that use single sign-on and even to electronically sign/seal Adobe PDF files. But I want to do something similar with files that are going outside the firewall. I can use my work certificate but the problem is if the people I send it to try to verify the signature, the authentication chain gets broken because our cert server is inside the firewall. They'll still see the JPG image of my signature but they won't be able to validate the digital portion (not that these folks are that bright anyway).

So then I thought about getting a personal digital certificate and haven't the foggiest idea of where to start (other than Google) or how much they cost? Or even if this is a practical thing to do?