Patreon themselves have acknowledged that the price difference is due to Apple and Google [charging] extra fees for in‑app purchases (almost 30%!) and they advise subscribing directly via their website to see the correct price.
What you can do to get the correct (lower) price:
Here are a few reliable workarounds:
• Use the mobile browser (not the app)
Visit patreon.com using Safari or Chrome on your device. When you subscribe there, the correct price will be displayed and applied.
£12 +VAT Moon Club
£32+VAT Moon Circle
£50+VAT Moon Coven
Use a desktop or Android device
Subscriptions initiated on a PC or Android app/browser will show the correct pricing without the 30% Apple markup.