You're straining my credibility with this "rich" bit. I have neither personal, anecdotal nor psychological research evidence to believ wealth comes within an order of magnitude of young or beautiful in its effects on attractiveness.
For those men who are honest with themselves about their desire to have nsa sex wit young beautiful women there's seekingarrangement.com
Curious as to why they have to be rich if the primary goal is no-strings-attached sex? If the assumed hope is that one could mooch off this rich, young, beautiful women a little before engaging in the no-strings-attached sex and taking one's leave, I'd say that would bring supply down to about zero.
Attractive females in the 18-25 bracket are pursued by men in the 18-death age bracket, far more than 18-25 year old men are pursued by women in the 18-death age bracket.
This leads to scarcity, and men use "rich", "high-status", "famous", etc. to differentiate themselves.
Male competition for breeding rights is the bedrock of human civilization (and probably for animals too)
Beyond the difficulties that you've mentioned you've got established competition who has plenty of ill gotten cash to spend plastering the web/world with ads. And as someone already mentioned people who have been scammed by a dating site are likely to keep that to themselves. Competition who will sing their own praises from the rooftops combined with quiet victims is a bad combination to have to compete with.
I realize it is difficult (chicken and egg, subtleties about dating/sex habits of males and females), but someone ought to be able to do it.