Each has a free trial period for evaluation. They are being sold via Freemius and will require a name, email, and a payment source for the free trail. Once the trial has expired your payment source will be billed the appropriate amount. You will be able to cancel the trial at any point during the trial period.
You can register for Free Trial for a premium add-on from the Add-Ons tab. You will be re-directed to the checkout page for the particular premium add-on and further instructions, along with a download link, will be provided by email.