Referrals Fee

Here is what I am looking for:

Have a feature on my customer's site where people can join because they have been referred by a local charity, and we would donate $1 for every person referred to the charity that referred them. Need to be able to know, though, where they came from (probably a dedicated link off an e-mail). It would be nice to have a “badge” on their profile that referenced the charity as well.

Any pointers of where can I start and what should I integrate will be of great help!!

Thanks
Rohit

i would look at an "affiliates" software or extension.