It is 20,000 baht or the equivalent in another currency, so if you are bringing USD cash money it will be fine. You hardly ever get asked, but always good to be prepared just in case.
Unfortunately the IO was correct you cannot change from a OA visa to a Non O visa in county. So you must leave Thailand, and either apply for the Non O visa in an embassy/ consulate or you can come back into Thailand on a visa exempt stamp the apply here for the Non O visa.
correct Brandon, I should have said if you qualify it isn’t a hard process. I have 15 friends that have achieved it , and I will be doing it myself next year, after 46 years traveling and living here, and being married to my Thai wife for the last 37 years and having had a work permit for the last 6 years.