Avplan web site has "The AvPlan app is available from the Apple App Store. The app price is free, with a one months unrestricted free trial of all features."
For both AVPLAN ans OzRunways it is best to buy the subscription from their web site (not the App Store), and just use App Store to install the program on the iPad. That is cheaper for the purchaser.
Both are excellent. Seems to me there is little between them. AVPLAN have just been announced as one of 2 apps in shortlist for a competition at Avalon Airshow "Congrats to two apps that have been shortlisted for Aerospace Australia innovation awards: AvPlan and Jacobson Flare". OzRunways also has excellent reviews.
Long may both companies thrive as we all benefit from them competing against each other so actively.