You are trying to buy the monthly subscription. But that isn’t necessary, just an option.
If you would like to buy the bundle just click on the amount you would like to pay (for example 1 Dollar) then scroll down on the page, enter your e-mail in the input field “Enter your email address here” and click either on “Pay with PayPal” or “Pay with Card”. That’s all. After you payed, you’ll receive an e-mail with the download link. No need to register or add something to a cart.