Spitzer’s family is really, really rich.
I think this has far more to do with the marginal utility of $4,000 than it has to do with the quality of the product. For some people, $4K is chump change. He probably paid that much in the hope that the woman and service would be discreet.
Of course, the irony of it all is that it was the moving of large sums of money that wound up tripping him up. If he had been bleeping out a couple hundred bucks out of the ATM to get a more reasonably priced hooker, he would never have been caught.