How To Provide Google Apps Email Account With Domain Mapping

I'm going to offer domain mapping to my customers, but would also like to be able to let them have an email address for their chosen domain.

Browsing through the forums it suggests Google Apps, but as it stands, google apps give only 10 free accounts per domain.

Does each domain mapped to my website count as their own domain?

If I setup the MX records in my cpanel and gave them instructions on adding a verification page on their site, would this allow each of my users to have their own free email account at their chosen domain name?