ChatGPT Plus is listed at $20 per 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 per month, but the actual price you pay can vary between about $13 and $27. This difference comes from extra fees like VAT or GST and app store markups on iOS and Android