Well, I don't know, but it's entirely conceivable to me given his income/assets and his probable desire to avoid the alternative of "shopping around" for bargains elsewhere. Price may not have been as important a factor to him as the illusion of a source that would help keep his activities a secret.
I don't know how long this relationship lasted or exactly how much was paid, but the sum you're quoting seems to me to be a fairly modest one for someone in his position. I'm sure that there's a lot of addicts who have more quickly spent much more.