I forgot to mention Security Extension would be needed as well.
I have created the download link page with Digital File Pro 2. I was thinking I could configure Security Assist extension to allow only logged in users created with the User Registration Solution Pack to access the download link page. I would need a way to get payment confirmation which would set a value in a database (AllowDownload). Somehow the download link page will only show up if the AllowDownload table has a value of 1.
Maybe this is a bit to much.