There is a cheaper option join up for free and buy the religious title of Reverend Doctor or Litterarum Doctor since these are on file as your religious title it would be like calling them a Rabbi or Cleric or Father or Imam etc. And would cost just $10.00. Add something in you can get an official clergy ID card with the title on it to show your professional title and standing as a member of the clergy. I will note the government will not go after a churches clergy titles since they are not used in an academic sense it would likely smack right up against the 1st Amendment protections. So lets see doing it this way with a card would cast maybe $25.00 and you can use the title doctors seems like a good option.