You can use Easy Paypal and Quick IPN to create a web site with paid registration.

In this scenario, Easy Paypal is used to create Paypal button and Quick IPN is used to process the payment.

Here is what you need to do to support paid user registration:

1. Remove register link option for login module.
2. Create a registration article with Easy Paypal button in it.
3. Configure Quick IPN to accept payment with automatically creating Joomla user account option. (Using the same item # as the Easy Paypal one)
4. Go to Paypal.com and configure the IPN notification to Quick IPN processing.
5. Create a menu link to point to the registration article.

Once configured, Quick IPN will automatically create a user account based on the payer email address, send the password to the user.