OK, You have described the way almost every dating/subscription website works.
There are so many questions about authentication systems for codeigniter, check this out for example:
How should I choose an authentication library for CodeIgniter?
I have only used ion auth - http://benedmunds.com/ion_auth/ and tanks auth - http://konyukhov.com/soft/tank_auth/, these seem to be the most popular with the biggest user bases. Both can be easily modified to have different levels of user access. In fact ion has this out of the box you just have to put in your own group checks. Personally I would build off the back of ion auth. Ion auth is a good lib which has only the basics, allowing you to set things up however you want. It is also in my opinion the easiest to work into an existing application due to it's minimal nature
However if you are looking for something which is going to come ready made, you could look at ezauth - http://ellislab.com/forums/viewthread/70386/. I seem to remember this access levels and an admin panel going on. Unfortunately the demos gone (never a good sign) and you may find it difficult to make changes to if it doesnt work exactly the way you want.