But was it appropriate, critics asked, for a former President to cash in on his White House luster so blatantly? Of the four living ex-Presidents, Jimmy Carter seems to have done the least for financial gain, spending his time instead on church-, housing-and peace-related efforts. Richard Nixon has published seven books, but accepts no honoraria for public appearances. Gerald Ford has turned himself into a one-man industry, producing endorsements, speeches and public appearances and serving on corporate boards; last year alone he earned an estimated $1 million. All that, however, pales next to Reagans $2 million single score in Japan. Says Henry F. Graff, a Columbia University professor who specializes in the Presidency: The founding fathers-Washington, Adams, Jefferson, Madisonwould have been stunned that an occupant of the highest office in this land turned it into bucks.