I work a lot with some scripts which are used to run paid-to-read (PTR) email email sites. The script is called Cash Crusader and is built in PHP Mysql. I believe it is one of the more complex PTR scripts available, but is also written clearly and I think will be understandable enough.
The script has some mail targetting features - so when the mails are sent out they can be sent to only certain members. This uses a system of Membership types, and mails can also be targetted according to countries or states. The job I have in mind is to add additional demographic fields (gender, date of birth, occupation) and have the scripts be able to target these for mail sendouts.
The scripts do have an inbuilt plugin interface, which may be useable for this job. I think after looking at the scripts, you will see it is not too big a job, but is beyond my own limited php/mysql abilities at this stage. I could do it I think, but it would take me too long as I am a beginner and I'd be very slow.
Please ask any questions you wish with PM's