Change $100 at a money exchange. The Super Rich money exchange usually has better exchange rates. You can find out the nearest location on Google when you get there. Just use Google translate which is in Chrome, to change the page to English. Make sure you take only new $100 bills, the kind with the ID strip and hologram. Keep them new and flat (they love no creases, bent corners or small tears) for the best exchange rate. Second best, but with some fees attached, is to use an ATM at a bank in one of the zillions of malls or Tesla Lotus market places.
I just read something sent by a friend that is in the Thai news. They are now working on a plan, at least for some tourists, to have bubble areas within Thailand. They are proposing several select areas where tourists can stay quarantined for 14 days while visiting the sites within the areas but not leaving for other areas. They were talking about a requirement of a specific type of covid testing just shortly before arrival which must be negative and then an additional test at the end of the 14 days to be able to go to other areas in Thailand. This apparently has not been passed yet but is moving through the chain of consideration.