Add registration authentication function to Wordpress Theme + plugin

I have a Wordpress theme and a plugin, and I want to setup registration for them so they cannot be used unless authenticated against my member database. WHen enabling the theme or activating the plkugin, I want it to ask for users email address. The email address needs to be checked against my member database--if user paid for product "x" then accept and activate. If they did not pay or email is not found, give them an error message and do not activate. The theme and plugin will authenticate against the same database but may have different product IDs to check against. So it is possible for a user to be able to activate 1 but not the other. My membership system is DAP Digital Access Pass (MySQL database) Please quote time + cost--I am ready to start NOW for right bidder.