Referral program

I wanted to request your services for some addition to my current website [login to view URL] If you have been to [login to view URL] , you must have seen their referral program where in a user can unlock his account by referring some new users to site who have not yet registered. I want to implement the same feature in my website , where I will offer the my candidates to referr upto 24 candidates to register and once I see 24 referrals from a particular candidate I will offer him free service of his/Her choice . In this , I should be able to get a notification about the users who have completed the 24 referrals in the admin section and at the same time the candiate has to be able to see how many users he has successfully referred thru his login. One thing is sure that my current database will have to connected in order to put a check for candidates who are already registered and inform the same to the candidate who is referring . I am sure you have understood my plan . I am open to your suggestions if any and also advise me the charges incurred & no of days