Thai Nationals don't need Covid test if they flying with Thai Airways, other airlines it's different, if fly with Thai Airways the SQ is free, for the present,COE is still required....as is a fit to fly certificate 72 hours valid to flight. This is what my fiance had.
Less than the rip offs some clinics charging £125 standard and £245 priority meaning hopefully guaranteeing you get test result back in 24hrs via email in your 3 days covid free days, £80 and test result back in an hour seems very reasonable.!