I will save you the hassle as I have done this already recently. Dont bother queing at patong immigration for a covid extension, you will be told and re directed to phukets main office immigration. And yes its 1900tbh regardless of duration.
its a frustrating situation, because although it's supposed to be the hotel or landlord that gets fined. Inevitably it is the tourist that gets fined when he or she tries to extend visa. So most Hotels landlords dont really care. All i can advise is try get the tm30 sorted however you can with ample room to breathe before you intend to extend your visa.
because you will find it difficult to get an extension without the tm30.. What will likely happen is you get fined on behalf of the hotel for them not filing the tm30, unfair but this is the nonsense thailand creates. I was in same situation last month.
just live frugally at the end of the day you got your family there which is everything to you, just cover the basics... Mrs and kids etc. But yeah its a cunt of a situation. But we knew this when we left the uk.