Where do I pay the 75 $ to get the e-mail with information to upgrade from demo version to full version?
If you want to acquire the application, then it's necessary to visit the official website. You have the possibility to download the latest released version as well as purchase the product's license. Visit the page through the link posted below.
Note: The website is using PayPal as payment method and it doesn't matter if you don't have an account because you can use you credit card to pay through PayPal.