I doubt he would have made much. The reality of book publishing is that only people who have huge bestsellers or multiple good-selling books make a lot - right at the top you have the J,K.Rowlings etc... who are selling hundreds of millions of copies.
This is why college textbooks cost so much. Too specific of a readership to make a profit from, without charging an arm and a leg.
P.S. Ray was a lovely man, I knew him for a little over a year shortly before everything that went down at Bethel. The tone of his books reflect his disappointment with the Watchtower Society rather than any resentment and dissent and they are a testament to his character and provide even more credibility to his situation.