What is the late fee for an entry stamp extension in Thailand?

I don’t think

that is the immigration office where you can receive “normal” visa or extension services.

That’s is an immigration detention center or some other immigration related facility I guess.

you wouldn't lose days of extension if you are going there in advance. Immigration officer adds +30 days from your last day of current stamp. (But you better to make it sure when you get the extension)

@Anikqua ********

I would say do your very best to get in there in to get your extension.

What you don't need or want is an overstay stamp in your passport. :O There's already one consulate in the area that won't give tourist visas if you have an overstay stamp in your passport.

If that isn't motivation enough to get in and get the extension before your current stamp expires I don't know what is ;)