I want to integrate PHP codes to my existing HTML.
It will take about 5~8 hours.
What you will need to do :
1. You will build up secure page that will be accessible by random passwords.
2. The secure page will be accessible if a user has a password.
3. After payment done, email will be sent with that password and redirect a user to the secure page.
This is simple, and won't take much time if you are a qualified developer.