It’s well documented in other posts on here that immigration seriously do not want to do extensions for a DTV. Although some have done so successfully I believe the hoops they had to jump through to do so will make them never want to do it again.
A money order or cheque isn’t going to help you. You need a Thai bank account with an 800k balance to get a retirement visa/extension. Depending on the office this may have to be seen as an international transfer.