Create a payment capture and integrate with webstie

I want to convert existing website (getfreedocs(dot)com from free to pay to access. Currently users visit site and register and their access is granted for free. I want to change to Pay to access with annual renewal. I have PayPal account so will want to setup API for this. Please view site and look at current source code as source of help and provide conservative bid convert. Currently users have to log in to access form pages to create documents.. I am fairly confident that can remain the same. the only thing that will need to be done is create gateway from front page to other pages requiring payment. Existing users have database, we will scrub those so all new users will require registration and prior payment before access. Please bid...