Which, by the way, is an idea that I'll be copyrighting very soon, just in case...

But all joking aside, yeah, it's not that hard to set up your own site with a cam, and a link/button with the right URI to have people pay the ammount.
Heck, you could even just set up an IRC channel or some chat messenger, and advertise that, using that as some form of "lobby" where you could pick the clients you want, maybe discuss payments and what they're expecting.
Heck, you could even team up with a few other freelancers so there'd always be someone available to do a show, thus causing more choice and opportunity for the clients, meaning a bit more client retainment, as well as opening up more ways of making a bit more for the entertainers.
But I might be thinking a bit too far ahead on these things, so let's just stick with the basic things.
(edited to correct a typo and add a smily)