ChatGPT Plus is listed at $20 a month, but the actual price you pay can vary...

https://smoothdecorator.com/why-did-openai-keep-chatgpt-plus-at-20-since-february-2023/

ChatGPT Plus is listed at $20 a month, but the actual price you pay can vary from about $13 to $27. This difference comes from added taxes like VAT or GST and extra fees from app stores like Apple or Google