The listed $20 price for ChatGPT Plus often varies between $13 and $27...

https://highstylife.com/i-keep-hitting-chatgpt-limits-should-i-start-a-new-thread/

The listed $20 price for ChatGPT Plus often varies between $13 and $27 depending on your location and platform. This difference mostly comes from taxes like VAT or GST and extra fees added by app stores on iOS and Android