We need following things to be done...
1) Paypal Integration. User will click button on website and will be taken to paypal payment page(Use IPN for this as we want to keep data of users on website).
2) After successful payment user will be taken to other page.(It may be internal page or external page i.e of different site or server, will confirm tomorrow).
3) Admin panel to check details of users who have paid and few reports like, no. of registered users, amount of payments etc.
Its not a big job for person who has done similar jobs earlier.
Timeline 1-2 days. Budget $50-$100