How much is the fee for extending a Covid visa in Thailand?

alright any way you look at this you're working illegally, period end of story.

There is no middle ground. you either have a Non-B visa/extension AND a valid work permit meaning you can work OR you don't. You need BOTH the correct visa and a work permit to legally work

You can't work once you've applied for a work permit until you get it, you can't work while you're waiting to get the paperwork to apply for the Non-B visa

ALL extensions inside the country no matter how long they're valid for are 1900baht.

If you are waiting for a work permit but working then you are working illegally.

You are asking about a 60 day unable to travel extension, no such thing as a Covid visa extension. This extension is 1900B

COVID extension costs 1,900 Thai baht

You are being asked for the cost of the W.P plus the Non B. 5000 baht.

Ok, first things first, you are working illegally. Secondly, all extensions are 1900 baht.