I don't think that "hundreds of thousands" is an unreasonable guess at all. Suzy was obviously the "golden girl," but she could scarcely be promoted as aggressively as she might have been as long as she was getting beaten every year by Regina. Here's one writer's take on the matter, back when the news about Regina was breaking:
http://sportsillustrated.cnn.com/2003/writers/mike_fish/11/25/hamilton/
"European meet promoters paid handsomely to draw Jacobs, the U.S. champion. Here at home, shoe giant Nike, with both runners under contract, wrote a fatter check to the champion than to the runner-up.
"'Certainly, Nike has used that against Suzy in negotiations,' Hamilton says.
"OK, Nike simply negotiated off the hard facts. Favor Hamilton has won only three 1,500-meter titles at the U.S. championships -- all when Jacobs wasn't in the race. Give her 11 national titles to go with her cover-girl looks and today she might rival Mia Hamm for commercial time and endorsements.
"There's no telling the sum of lost money we're talking about. Just in Nike bonuses, alone, it's $150,000."