Bill,
I am going to guess that Flynn felt he was up against Raynor and wanted to subtly distinguish his style from theirs - i.e., broad, natural slopes vs. manufactured ones.
He may have had an inkling that his courses cost more, but if it was a letter to the Rockerfellers, he might also have presumed that product would drive the decision more than bottom dollar. In fact, he might have believed that they would want to buy a more expensive course, equating it with "better" regardless of relative general cost differences between architects.
Raynor was an engineer, but Toomey and Flynn are, I believe, generally credited with the earliest engineering bid quantities, etc. and could offset a higher known cost against supposedly less accurate lower estimates.
Again, just a guess.
BTW, assuming human nature doesn't change, those seeking professional services are more likely to select a firm on creativity and quality over price. If they are doing a second project, they tend to stick with the same consultant, providing they have a good experience, because they are then more comfortable that the project can be delivered on budget.