ChatGPT Plus has a listed price of $20, but the actual cost you pay can vary...

https://cesarsuniquenews.theburnward.com/why-do-referral-codes-not-stack-for-chatgpt-plus-trials

ChatGPT Plus has a listed price of $20, but the actual cost you pay can vary from about $13 to $27. This difference happens because of taxes like VAT or GST and extra fees added by app stores on iOS and Android