My card will be charged $5 if I make an account. It does not say what the frequency of billing is $5 a year , month, or minute.
Edit: unless they are crazy well-priced, like this dictionary app https://apps.apple.com/us/app/dict-cc-dictionary/id327732352 (1 euro per year!)
Fantastical comes to mind first. Used to be like 5€ on the App Store, now it's 3.67€/month.
For Android apps I'm torn. It's actually a continuous effort to keep your app workable on new versions, but Android keeps my purchases from phone to phone.