Depends how much you are using it - for a casual user the $20 tier gives you just about enough use for hobby projects etc.

Or if you are doing full time development then you just need to pony up for the 20x tier if you want to use it.

Running Codex locally removes so much friction and is so fast compared to either running it on the web (where it has to build environments online etc which consumes time) or compared to copy-pasting chatgpt that it's just a no-brainer.

I don't know about Chatgpt but I used Kimi (they have a Chinese-only plugin that does desktop control - works fine if you enable it even if you don't know Chinese). Observing how it works, it's mostly using the accessibility features of the user interfaces - it fetches a sort of DOM for the desktop applications. Only rarely it has to take a screenshot.